Fast transient supply with a separated high frequency and low frequency path signals

ABSTRACT

A power interface device includes a main switching converter and an auxiliary switching converter. The main switching converter is coupled to an input terminal and an output terminal and configured to operate at a first switching frequency to source a low frequency current from the input terminal to the output terminal. The auxiliary switching converter is coupled to the input terminal and the output terminal in parallel with the main switching converter and configured to operate at a second and higher switching frequency than the first switching frequency to source a fast transient high frequency current from the input terminal to the output terminal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from U.S. ProvisionalApplication Ser. No. 62/280,897, filed Jan. 20, 2016, and entitled“Control Architecture With Improved Transient Response” and U.S.Provisional Application Ser. No. 62/280,878, filed Jan. 20, 2016, andentitled “Fast Transient Power Supply With a Separated High Frequencyand Low Frequency Path Signals,” which are incorporated by referenceherein in their entirety.

BACKGROUND

A power supply system includes a power source, a load device, and apower interface device connecting the electrical power source to theload device. The power source may include a battery, a power grid, asolar photovoltaic cell, an AC generator, and/or an output of front-endpower converter. The power interface device may be configured toincrease or decrease the voltage of the power source to provide asuitable voltage for the load device. The power interface device may bea boost converter or a buck converter or any other converter. The loaddevice may include a resistive load, a magnetic load, a capacitive load,a heater. In one implementation, the load device may be a low voltagebut a high current load device such as, for example, computer centralprocessing unit (CPU). This type of load device may have many loadtransient conditions.

During a load transient condition, the current of the load device maysubstantially change within a very short time period. For example,during the transient condition, the current of the load device mayincrease from 0 A to 100 A, or decrease from 100 A to 0 A, in less thanone microsecond. These sudden changes in current can create largevoltage variation at the load device and can cause the output voltage toswing outside of the regulated operating window of the load device.

To minimize transient variations, in one implementation, a large powercapacitor may be added to the output of the power supply system. Thecapacitor may source or sink the necessary current during the transientcondition and therefore reduce voltage variation caused by the loadtransient. To this end, the output capacitor is useful in supplementingthe converter's slowly rising current to meet the increase in currentdemand from the load device. Similarly, the output capacitor is usefulin sinking the current to meet the sudden decrease in current from theload device. Capacitors, however, are expensive and as such may increasecost or size of the system.

In another implementation, the converter may be pushed to run at ahigher bandwidth to respond to a load transient quickly. However, aswitching mode converter bandwidth is limited by its switchingfrequency. Therefore, to push the converter to run at the higherbandwidth, the converter has to operate at a higher switching frequency.This means more power loss because each time there is a turn on/off ofthe switch, there is a power loss. As such, the power supply system isalso limited by the power loss of the power converter placed between thepower source and the load device.

Hence, a need exists for a power supply system capable of providing afast response to the transient condition of the load device whileincreasing the efficiency and reducing costs and size.

SUMMARY

In one general aspect, the instant application describes a powerinterface device coupled to a power source at an input terminal and aload device at an output terminal and configured to change a voltage ofthe power source to correspond a voltage associated with the loaddevice. The power interface device includes a main switching convertercoupled to an input terminal and an output terminal and configured tooperate at a first switching frequency to source current from the inputterminal to the output terminal; an auxiliary switching convertercoupled to the input terminal and the output terminal in parallel withthe main switching converter and configured to operate at a second andhigher switching frequency than the first switching frequency to sourcecurrent from the input terminal to the output terminal; a feedback andcompensation circuit configured to detect a transient condition at theoutput terminal and output a transient signal based on the detectedtransient condition; a main control circuit including a low pass filterconfigured to receive the transient signal and output a lower frequencycomponent of the transient signal, the main control circuit configuredto generate a main control signal based on the lower frequency componentof the transient signal for controlling the main switching converter; anauxiliary control circuit including a high pass filter configured toreceive the transient signal and output a higher frequency component ofthe transient signal, the auxiliary control circuit configured togenerate an auxiliary control signal based on the higher frequencycomponent of the transient signal for controlling the auxiliaryswitching converter; and a common buffer commonly shared by the maincontrol circuit and the auxiliary control circuit. The common bufferincludes an input terminal and an output terminal. The input terminal ofthe common buffer is connected to the feedback and compensation circuit.The output terminal of the common buffer is connected to the high passfilter and the low pass filter.

The above general aspect may include one or more of the followingfeatures. For example, the feedback and compensation circuit mayinclude: a feedback sense circuit configured to sense an output voltageat the output terminal; an error amplifier configured to receive thesensed output voltage and a reference voltage and output the transientsignal based on the sensed output voltage and the reference voltage; anda compensation circuit configured to receive the transient signal andoutput a frequency compensated transient signal to the common buffer.The feedback sense circuit may include a plurality of resistors andcapacitors configured to sense the output voltage and generate afeedback voltage. The error amplifier may be configured to receive thefeedback voltage and the reference voltage, and generate the transientsignal when the feedback voltage and the reference voltage are notsubstantially equal to each other.

The compensation circuit may include a first capacitor, a secondcapacitor, and a resistor. The first capacitor may be connected at oneend to an output terminal of the error amplifier and at another endbeing connected to a ground terminal. The second capacitor may beconnected in series with the resistor forming a seriescapacitor-resistor network. The series capacitor-resistor network may beconnected at one end to the ground terminal and at another end to theoutput terminal of the error amplifier.

The common buffer may be configured to isolate the main control circuitand the auxiliary control circuit from an impedance of the feedback andcompensation circuit. The main control circuit may further include amain comparator configured to compare the lower frequency component ofthe transient signal with a sensed low frequency inductor signal sourcedby the main switching converter and generate the main control signal forcontrolling the main switching converter. The main control signal mayenable the main switching converter to source to the output terminal alow frequency current tracking the lower frequency component of thetransient signal.

The low pass filter may include a resistor and a capacitor. The resistorof the low pass filter may be connected at one end to the common bufferand at another end to the capacitor of the low pass filter and anon-inverting terminal of the main comparator. The capacitor of the lowpass filter may be connected at one end to the resistor of the low passfilter and the non-inverting terminal of the main comparator and atanother end is connected to the ground terminal.

The auxiliary control circuit may further include an auxiliarycomparator configured to compare the higher frequency component of thetransient signal with a sensed high frequency inductor signal sourced bythe auxiliary switching converter and generate the auxiliary controlsignal for controlling the auxiliary switching converter. The auxiliarycontrol signal may enable the auxiliary switching converter to source tothe output terminal a high frequency current tracking the higherfrequency component of the transient signal.

The high pass filter may include a resistor and a capacitor. Thecapacitor of the high pass filter may be connected at one end to thecommon buffer and at another end to the resistor of the high pass filterand a non-inverting terminal of the auxiliary comparator. The resistorof the high pass filter may be connected at one end to the capacitor ofthe high pass filter and the non-inverting terminal of the auxiliarycomparator and at another end is connected to the ground terminal.

The main switching converter and the auxiliary switching converter mayinclude step-down, current mode, switching regulators configured toconvert a higher input voltage of the input terminal to a lower outputvoltage of the output terminal. The main switching converter may includea first main switch, a second main switch, a main inverter, and a maininductor. A drain of the first main switch may be connected to the inputterminal; a source of the first main switch may be connected to a mainnode; and a gate of the first main switch may be connected to the maincontrol circuit and configured to receive the main control signal. Adrain of the second main switch may be connected to the main node; asource of the second main switch may be connected to the groundterminal; and a gate of the second main switch may be connected to themain inverter and configured to receive an inverse of the main controlsignal.

The auxiliary switching converter may include a first auxiliary switch,a second auxiliary switch, an auxiliary inverter, and an auxiliaryinductor. A drain of the first auxiliary switch may be connected to theinput terminal; a source of the first auxiliary switch may be connectedto an auxiliary node; and a gate of the first auxiliary switch may beconnected to the auxiliary control circuit and configured to receive theauxiliary control signal. A drain of the second auxiliary switch may beconnected to the auxiliary node; a source of the second auxiliary switchmay be connected to the ground terminal; and a gate of the secondauxiliary switch may be connected to the auxiliary inverter andconfigured to receive an inverse of the auxiliary control signal.

The main switching converter may be configured to source to the outputterminal low frequency current during the transient condition andoutside the transient condition. The auxiliary switching converter maybe configured to source to the output terminal high frequency currentduring the transient condition and substantially zero average currentoutside the transient condition. The transient condition may include asudden increase or decrease in load current, or a sudden increase ordecrease of an output voltage. The first and second main switches andthe first and second auxiliary switches may include FET switches.

In another general aspect, the instant application describes anotherpower interface device comprising a main switching converter coupled toan input terminal and an output terminal and configured to operate at afirst switching frequency to source current from the input terminal tothe output terminal; an auxiliary switching converter coupled to theinput terminal and the output terminal in parallel with the mainswitching converter and configured to operate at a second and higherswitching frequency than the first switching frequency to source currentfrom the input terminal to the output terminal; a feedback andcompensation circuit coupled to the output terminal and configured todetect a transient condition at the output terminal and output atransient signal based on the detected transient condition; a maincontrol circuit coupled to the feedback and compensation circuit and themain switching converter and configured to receive the transient signalfrom the feedback and compensation circuit and to generate a maincontrol signal based on the transient signal for controlling the mainswitching converter; a low pass filter coupled to the feedback andcompensation circuit and configured to receive the transient signal fromthe feedback and compensation circuit and output a lower frequencycomponent of the transient signal; an adder circuit coupled to the lowpass filter and the feedback and compensation circuit and configured toreceive the lower frequency component of the transient signal from thelow pass filter and the transient signal from the feedback andcompensation circuit and output a higher frequency component of thetransient signal; and an auxiliary control circuit coupled to the addercircuit and the auxiliary switching converter and configured to receivethe higher frequency component of the transient signal and generate anauxiliary control signal based on the higher frequency component of thetransient signal for controlling the auxiliary switching converter.

The above general aspect may include one or more of the followingfeatures. The adder circuit may be configured to receive the lowerfrequency component of the transient signal from the low pass filter atits inverting terminal and the transient signal from the feedback andcompensation circuit at its non-inverting terminal, subtract the lowerfrequency component of the transient signal from the transient signal,and output the higher frequency component of the transient signal to theauxiliary control circuit.

The power interface device may further include a common buffer commonlyshared by the main control circuit and the auxiliary control circuit andconfigured to isolate the main control circuit and the auxiliary controlcircuit from an impedance of the feedback and compensation circuit. Thelow pass filter may include a resistor and a capacitor. The resistor maybe coupled to an output terminal of the feedback and compensationcircuit at one end and to a first node at a second end. The capacitormay be connected to the first node at one end and to a ground terminalat another end. The adder circuit may be coupled to the first node atits inverting terminal and to the output terminal of the feedback andcompensation circuit at its non-inverting terminal and configured toreceive the lower frequency component of the transient signal from thelow pass filter at the inverting terminal and the transient signal atthe non-inverting terminal and output the higher frequency component ofthe transient signal to the auxiliary control circuit.

The power interface device may further include a plurality of resistorsconfigured to provide a gain factor for the higher frequency componentof the transient signal; and an offset voltage source configured tooffset high frequency current sourced by the auxiliary switchingconverter outside the transient condition during a steady state toenable sourcing substantially zero average current from the auxiliaryswitching converter. The plurality of resistors may include a firstresistor connected to the non-inverting terminal of the adder circuitand a second resistor connected to the inverting terminal of the addercircuit. The offset voltage source may be coupled to the non-invertingterminal of the adder circuit through the first resistor.

In another general aspect, the instant application describes a powerinterface device comprising: a main switching converter coupled to aninput terminal and an output terminal and configured to operate at afirst switching frequency to source current from the input terminal tothe output terminal; an auxiliary switching converter coupled to theinput terminal and the output terminal in parallel with the mainswitching converter and configured to operate at a second and higherswitching frequency than the first switching frequency to source currentfrom the input terminal to the output terminal; a feedback andcompensation circuit coupled to the output terminal and configured todetect a transient condition at the output terminal and output atransient signal based on the detected transient condition; a high passfilter coupled to the feedback and compensation circuit and configuredto receive the transient signal from the feedback and compensationcircuit and output a higher frequency component of the transient signal;an adder circuit coupled to the high pass filter and the feedback andcompensation circuit and configured to receive the higher frequencycomponent of the transient signal from the high pass filter and thetransient signal from the feedback and compensation circuit and output alower frequency component of the transient signal; a main controlcircuit coupled to the adder circuit and to the main switching converterand configured to generate a main control signal based on the lowerfrequency component of the transient signal for controlling the mainswitching converter; and an auxiliary control circuit coupled to thehigh pass filter and the auxiliary switching converter and configured togenerate an auxiliary control signal based on the higher frequencycomponent of the transient signal for controlling the auxiliaryswitching converter.

In another general aspect, the instant application describes a powerinterface device comprising: a main switching converter coupled to afirst input terminal and an output terminal and configured to operate ata first switching frequency to source current from the first inputterminal to the output terminal; an auxiliary switching convertercoupled to a second input terminal and the output terminal andconfigured to operate at a second and higher switching frequency thanthe first switching frequency to source current from the second inputterminal to the output terminal; a feedback and compensation circuitcoupled to the output terminal and configured to detect a transientcondition at the output terminal and output a transient signal based onthe detected transient condition; a main control circuit coupled to thefeedback and compensation circuit and the main switching converter andconfigured to receive the transient signal from the feedback andcompensation circuit and to generate a main control signal based on thetransient signal for controlling the main switching converter; and anauxiliary control circuit including a first gain buffer coupled to thefeedback and compensation circuit and configured to amplify thetransient signal received from the feedback and compensation circuit, ahigh pass filter coupled to the first gain buffer and configured toreceive the amplified transient signal from the first gain buffer andoutput a higher frequency component of the amplified transient signal,and an auxiliary comparator coupled to the high pass filter andconfigured to receive the higher frequency component of the transientsignal at a first terminal and a sensed high frequency inductor signalsourced by the auxiliary switching converter at a second terminal andgenerate an auxiliary control signal based on comparison result of thehigher frequency component and the sensed high frequency inductor signalfor controlling the auxiliary switching converter.

The above general aspect may include one or more of the followingfeatures. The power interface device further may include an offsetvoltage source coupled to the high pass filter and configured to offsethigh frequency current sourced by the auxiliary switching converter toenable sourcing substantially zero average current from the auxiliaryswitching converter outside of the transient condition.

A power supply system may include a first power source coupled to thefirst input terminal; a second power source coupled to the second inputterminal; a load device coupled to the output terminal. The powerinterface device described above may be coupled to the first and secondpower sources and the load device and configured to adjust a voltage ofthe first power source to correspond to a voltage of the load device.The first power source is coupled to the main switching converter. Thesecond power source may be coupled to the auxiliary switching converterand may be independent from the first power source. The second powersource may include a capacitor.

The power supply system may further include an input source feedback andregulation circuit connected at one end to the second power source andat another end to the auxiliary control circuit for controlling theauxiliary switching converter. The input source feedback and regulationcircuit may include a feedback voltage sense circuit, an erroramplifier, and a compensation circuit. The feedback voltage sensecircuit may be configured to sense the voltage of the second powersource through a network of first and second resistors and output afeedback voltage to an inverting terminal of the error amplifier. Thefirst resistor may be coupled to the second power source at one end andat another end is coupled to the inverting terminal of the erroramplifier and to the second resistor. The second resistor may be coupledto the inverting terminal of the error amplifier and to the firstresistor at one end and at another end is coupled to the groundterminal. The error amplifier may be configured to monitor the feedbackvoltage received at the inverting terminal of the error amplifier and areference voltage received at an non-inverting terminal of the erroramplifier and output a control signal when the feedback voltage is notsubstantially equal to the reference voltage.

The compensation circuit may include a first and second capacitors and aresistor. The first capacitor may be connected at one end to an outputof the error amplifier and at another end to the ground terminal. Theresistor of the compensation circuit may be connected at one end to theoutput of the error amplifier and at another end to the secondcapacitor. The second capacitor at one end may be connected to theresistor of the compensation circuit and at another end to the groundterminal.

The auxiliary control circuit may further include a second invertinggain buffer having an input terminal and an output terminal. The inputterminal of the second gain buffer may be connected to the outputterminal of the error amplifier, which regulates a voltage of the secondpower source. The output terminal of the second gain buffer may beconnected to the high pass filter. When the voltage of the second powersource falls below the reference voltage, the error amplifier mayincrease the control signal, thereby decreasing signal on the firstterminal of the auxiliary comparator through the second gain bufferwhich in turn results in current flowing from the output terminalthrough the auxiliary switching converter to the second power source tocharge the second power source.

In another general aspect, the instant application describes a powerinterface device comprising: a main switching converter coupled to aninput terminal and an output terminal and configured to operate at afirst switching frequency to source current from the input terminal tothe output terminal; an auxiliary switching converter coupled to theinput terminal and the output terminal in parallel with the mainswitching converter and configured to operate at a second and higherswitching frequency than the first switching frequency to source currentfrom the input terminal to the output terminal; a feedback andcompensation circuit coupled to the output terminal and configured todetect a transient condition at the output terminal and output atransient signal based on the detected transient condition; a firstbuffer coupled to an output terminal of the feedback and compensationcircuit; a low pass filter including a resistor and a capacitor, whereinthe resistor is coupled to an output terminal of the first buffer at oneend and to a first node at another end and the capacitor is coupled tothe first node at one end and to a ground terminal at another end; amain control circuit including a main comparator circuit having a firstinput terminal and a second input terminal.

The first input terminal is coupled to the first node. The second inputterminal is coupled to a sensed inductor current signal of the mainswitching converter. The main comparator circuit is configured toreceive a lower frequency component of the transient signal from the lowpass filter at the first input terminal and sensed inductor currentsignal at the second input terminal and generate a main control signalbased on the lower frequency component of the transient signal forcontrolling the main switching converter. The auxiliary control circuitincludes a gain buffer and an auxiliary comparator having a first inputterminal and a second input terminal. The gain buffer includes aninverting terminal coupled to the output of the first buffer and anoninverting terminal coupled to the first node and configured to outputa higher frequency component of the transient signal to the first inputterminal of the auxiliary comparator. The auxiliary comparator isconfigured to compare the higher frequency component of the transientsignal received at the first input terminal and a sensed high frequencyinductor current sourced by the auxiliary switching converter andreceived at the second input terminal and generate an auxiliary controlsignal for controlling the auxiliary switching converter.

The above general aspect may include one or more of the followingfeatures. During a load step up transient condition, the auxiliarycomparator may generate a high auxiliary control signal for sourcinghigh frequency current from the input terminal to the output terminal toimprove transient response and reduce output voltage ripple due to thetransient condition and the main comparator generates a high maincontrol signal for sourcing low frequency current from the inputterminal to the output terminal. The high frequency current may trackthe higher frequency component of the transient signal. The lowfrequency current may track the lower frequency component of thetransient signal.

During a load step up transient condition, the auxiliary comparator maygenerate a high auxiliary control signal for sourcing high frequencycurrent from the input terminal to the output terminal to improvetransient response and reduce output voltage ripple due to the transientcondition and the main comparator generates a high main control signalfor sourcing low frequency current from the input terminal to the outputterminal. The high frequency current may track the higher frequencycomponent of the transient signal. The low frequency current may trackthe lower frequency component of the transient signal.

In another general aspect, the instant application describes a powerinterface device comprising: a main switching converter coupled to aninput terminal and an output terminal and configured to operate at afirst switching frequency to source current from the input terminal tothe output terminal; an auxiliary switching converter coupled to theinput terminal and the output terminal in parallel with the mainswitching converter and configured to operate at a second and higherswitching frequency than the first switching frequency to source currentfrom the input terminal to the output terminal; a feedback andcompensation circuit coupled to the output terminal and configured todetect a transient condition at the output terminal and output atransient signal based on the detected transient condition; a maincontrol circuit configured to receive the transient signal from thefeedback and compensation circuit and generate a main control signalbased on the transient signal for controlling the main switchingconverter; and an auxiliary control circuit configured to receive ahigher frequency component of the transient signal from the feedback andcompensation circuit and generate an auxiliary control signal based onthe higher frequency component of the transient signal for controllingthe auxiliary switching converter.

The feedback and compensation circuit includes: a feedback sense circuitconfigured to sense an output voltage at the output terminal andgenerate a feedback voltage, an error amplifier configured to receivethe feedback voltage and a reference voltage and output the transientsignal based on the sensed output voltage and the reference voltage, anda compensation circuit including a first capacitor, a second capacitor,and a resistor, the first capacitor coupled to an output of the erroramplifier at one end and to a ground terminal at another end, the secondcapacitor coupled to the output of the error amplifier at one end and tothe resistor at another end, the resistor coupled to the secondcapacitor at one end and to the ground terminal at another end. Theauxiliary control circuit includes an auxiliary comparator configured toreceive a higher frequency component of the transient signal from acrossthe resistor and sensed high frequency inductor current from theauxiliary switching converter and output the auxiliary control signalfor controlling the auxiliary switching converter.

In another general aspect, the instant application describes a powerinterface device comprising: a main switching converter coupled to aninput terminal and an output terminal and configured to operate at afirst switching frequency to source current from the input terminal tothe output terminal; an auxiliary switching converter coupled to theinput terminal and the output terminal and configured to operate at asecond and higher switching frequency than the first switching frequencyto source current from the input terminal to the output terminal; afeedback and compensation circuit coupled to the output terminal andconfigured to detect a transient condition at the output terminal andoutput a transient signal based on the detected transient condition; amain control circuit coupled to the feedback and compensation circuitand the main switching converter and configured to generate a maincontrol signal based on the transient signal for controlling the mainswitching converter; a resistor-capacitor (“RC”) and adder networkcoupled to the feedback and compensation circuit and configured toreceive the transient signal from the feedback and compensation circuitand output a higher frequency component of the transient signal; and anauxiliary control circuit coupled to the RC and adder network and theauxiliary switching converter and configured to receive the higherfrequency component of the transient signal and generate an auxiliarycontrol signal based on the higher frequency component of the transientsignal for controlling the auxiliary switching converter.

The above general aspect may include one or more of the followingfeatures. The RC and adder network may include a high pass filter and anadder circuit. The high pass filter may be coupled to the feedback andcompensation circuit and configured to receive the transient signal fromthe feedback and compensation circuit and output the higher frequencycomponent of the transient signal to the auxiliary control circuit. Theadder circuit may be coupled to the high pass filter and the feedbackand compensation circuit and configured to receive the higher frequencycomponent of the transient signal from the high pass filter and thetransient signal from the feedback and compensation circuit and output alower frequency component of the transient signal to the main controlcircuit. The main control circuit may be configured to generate the maincontrol signal based on the lower frequency component of the transientsignal.

The RC and adder network may include a low pass filter and an addercircuit. The low pass filter may be coupled to the feedback andcompensation circuit and configured to receive the transient signal fromthe feedback and compensation circuit and output a lower frequencycomponent of the transient signal. The adder circuit may be coupled tothe low pass filter and the feedback and compensation circuit andconfigured to receive the lower frequency component of the transientsignal from the low pass filter and the transient signal from thefeedback and compensation circuit and output the higher frequencycomponent of the transient signal to the auxiliary control circuit.

In another general aspect, the instant application describes a powersupply system comprising: a main switching converter coupled to a firstinput terminal and an output terminal and configured to operate at afirst switching frequency to source current from the first inputterminal; an auxiliary switching converter coupled to a second inputterminal and configured to operate at a second and higher switchingfrequency than the first switching frequency to source current from thesecond input terminal; a main control loop at one end coupled to theoutput terminal and at another end coupled to the main switchingconverter and configured to detect a transient condition at the outputterminal and generate a main control signal based on the detectedtransient condition for controlling the main switching converter; and anauxiliary control loop coupled to the auxiliary switching converter andconfigured to detect a transient condition and generate an auxiliarycontrol signal based on the detected transient condition for controllingthe auxiliary switching converter. The auxiliary control loop includesan auxiliary feedback and compensation circuit, a first gain buffer, ahigh pass filter, and an auxiliary comparator. The auxiliary feedbackand compensation circuit is configured to detect the transient conditionand output an auxiliary transient signal based on the detected transientcondition. The first gain buffer is coupled to the auxiliary feedbackand compensation circuit and configured to amplify the auxiliarytransient signal received from the auxiliary feedback and compensationcircuit. The high pass filter is coupled to the first gain buffer andconfigured to receive the amplified auxiliary transient signal from thefirst gain buffer and output a higher frequency component of theamplified auxiliary transient signal. The auxiliary comparator iscoupled to the high pass filter and configured to receive the higherfrequency component of the auxiliary transient signal at a firstterminal and a sensed high frequency inductor signal sourced by theauxiliary switching converter at a second terminal and generate theauxiliary control signal based on comparison result of the higherfrequency component and the sensed high frequency inductor signal forcontrolling the auxiliary switching converter.

The above general aspect may include one or more of the followingfeatures. The main control loop may include: a main feedback andcompensation circuit coupled to the output terminal and configured todetect the transient condition at the output terminal and output a maintransient signal based on the detected transient condition, and a maincomparator coupled to the main feedback and compensation circuit and themain switching converter and configured to receive the main transientsignal from the main feedback and compensation circuit and generate themain control signal based on the main transient signal for controllingthe main switching converter.

The auxiliary switching converter at one end may be coupled to theoutput terminal and at another end may be coupled to the second inputterminal. The auxiliary feedback and compensation circuit may be coupledto the output terminal and configured to detect the transient conditionat the output terminal and output the auxiliary transient signal basedon the detected transient condition.

The auxiliary control loop may further include a second inverting gainbuffer including an input terminal and an output terminal. The outputterminal of the second gain buffer may be connected to the high passfilter.

The power supply system may also include an input source feedback andregulation circuit connected at one end to the second input terminal andat another end to the input of the second gain buffer for controllingthe auxiliary switching converter. The input source feedback andregulation circuit may include a feedback voltage sense circuit, anerror amplifier, and a compensation circuit. The feedback voltage sensecircuit may be configured to sense the voltage at the second inputterminal through a network of first and second resistors and output afeedback voltage to an inverting terminal of the error amplifier. Thefirst resistor may be coupled to the second input terminal at one endand at another end may be coupled to the inverting terminal of the erroramplifier and to the second resistor. The second resistor may be coupledto the inverting terminal of the error amplifier and to the firstresistor at one end and at another end may be coupled to the groundterminal. The error amplifier may be configured to monitor the feedbackvoltage received at the inverting terminal of the error amplifier and areference voltage received at an non-inverting terminal of the erroramplifier and output a control signal when the feedback voltage is notsubstantially equal to the reference voltage. The input terminal of thesecond gain buffer may be connected to the output of the error amplifierwhich regulates the voltage at the second input terminal.

The compensation circuit may include a first and second capacitors and aresistor. The first capacitor may be connected at one end to an outputof the error amplifier and at another end to the ground terminal. Theresistor of the compensation circuit may be connected at one end to theoutput of the error amplifier and at another end to the secondcapacitor, and the second capacitor at one end may be connected to theresistor of the compensation circuit and at another end to the groundterminal.

When the voltage at the second input terminal falls below the referencevoltage, the error amplifier may increase the control signal, therebydecreasing signal on the first terminal of the auxiliary comparatorthrough the second gain buffer which in turn results in current flowingfrom the output terminal through the auxiliary switching converter to anauxiliary power source connected to the second input terminal to chargethe auxiliary power source. The auxiliary power source may include acapacitor.

The power supply system may further include a main power source coupledto the first input terminal; an auxiliary power source coupled to thesecond input terminal; and a load device coupled to the output terminal.The main power source may be coupled to the main switching converter.The auxiliary power source may be coupled to the auxiliary switchingconverter and may be independent from the first power source. The mainswitching converter may be configured to change a voltage of the mainpower source to correspond to a voltage of the load device.

The auxiliary switching converter may be placed on a same packing as theload device. The auxiliary switching converter may be connected at oneend to the first input terminal and at another end is connected to thesecond input terminal. The auxiliary feedback and compensation circuitmay be coupled to the first input terminal and configured to detect thetransient condition at the first input terminal and output the auxiliarytransient signal based on the detected transient condition at the firstinput terminal. The transient condition at the first input terminal mayinclude temporary loss of voltage at the first input terminal.

BRIEF DESCRIPTION OF DRAWINGS

The drawing figures depict one or more implementations in accord withthe present teachings, by way of example only, not by way of limitation.In the figures, like reference numerals refer to the same or similarelements.

FIG. 1 illustrates an exemplary power supply system configured to have afast transient response and a high efficiency;

FIGS. 2A and 2B illustrate an exemplary power supply system including amain switching converter and an auxiliary switching converter;

FIGS. 3(A)-3(E) illustrate exemplary waveforms associated with the powersupply system shown in FIGS. 2A-2B;

FIG. 4 illustrates another exemplary power supply system including amain switching converter and an auxiliary switching converter;

FIG. 5 illustrates another exemplary power supply system including amain switching converter and an auxiliary switching converter;

FIG. 6 illustrates an exemplary circuit diagram of the power supplysystem shown in FIG. 5 having a fast transient response;

FIG. 7 illustrates an exemplary simulation circuit diagram for thecontrol mechanism of the power supply system shown in FIG. 6;

FIGS. 8A-8C illustrate exemplary load transient simulation waveforms forthe circuit diagram shown in FIG. 6;

FIG. 9A illustrates a feedback loop gain comparison between a firstpower supply system including two phase buck switching converters and asecond power supply system including two phase buck switching convertersin parallel with an auxiliary switching converter;

FIG. 9B illustrates feedback loop phase margins for the first powersupply system and the second power supply system of FIG. 9A;

FIG. 10 illustrates another exemplary power supply system including amain switching converter and an auxiliary switching converter;

FIG. 11 illustrates an exemplary circuit diagram including twoindependent control mechanisms for a power supply system of the instantapplication;

FIG. 12 illustrates another exemplary circuit diagram for the controlloop of the power supply system shown in FIG. 6;

FIGS. 13A-13C illustrate exemplary load transient simulation waveformsfor the power supply system 600 controlled by the control mechanismshown in FIG. 12;

FIG. 14A illustrates another exemplary power supply system including twoseparate control signals for driving the main switching converter andthe auxiliary switching converter;

FIG. 14B illustrates another exemplary power supply system including twoseparate control signals for driving the main switching converter andthe auxiliary switching converter;

FIG. 15 illustrates an exemplary circuit diagram for the power supplysystem shown in FIG. 14A having a fast transient response;

FIG. 16A illustrates an exemplary simulation circuit diagram 1600 forthe power system shown in FIG. 15;

FIG. 16B illustrates a load transient performance comparison between afirst power supply system having single phase lower frequency buckconverter for handling both the lower frequency and higher frequencycomponents of the transient signal and a second power supply systemshown in FIG. 16A having a single phase lower frequency converter forhandling lower frequency component of the transient signal and a higherfrequency converter for handling high frequency component of thetransient signal;

FIG. 17 illustrates another exemplary circuit diagram of a feedbackcontrol mechanism configured to control a power supply system having amain switching converter and an auxiliary switching converter;

FIGS. 18A-18C illustrate exemplary load transient simulation waveformsfor the power supply system controlled by the feedback control mechanismshown in FIG. 17;

FIG. 19 illustrates another exemplary circuit diagram of a feedbackcontrol mechanism configured to control a power supply system having amain switching converter and an auxiliary switching converter;

FIGS. 20A-20C illustrate exemplary load transient simulation waveformsfor the power supply system controlled by the feedback control mechanismshown in FIG. 19;

FIG. 21A illustrates another exemplary circuit diagram of a feedbackcontrol mechanism configured to a power supply system having a mainswitching converter and an auxiliary switching converter;

FIGS. 21B-21D illustrate exemplary load transient simulation waveformsfor the power supply system controlled by the feedback control mechanismshown in FIG. 21A;

FIG. 22 illustrates another exemplary power supply system including twoseparate control signals for driving a main switching converter and anauxiliary switching converter;

FIG. 23 illustrates an exemplary power supply system similar to thepower supply system shown in FIG. 22 expect that the auxiliary switchingconverter has a separate power source;

FIG. 24 illustrates an exemplary circuit diagram for the power supplysystem shown in FIG. 23;

FIGS. 25A-25C illustrate exemplary load transient simulation waveformsfor the power supply system shown in FIG. 24;

FIG. 26 illustrates another exemplary power supply system including twoseparate control signals for driving a main switching converter and anauxiliary switching converter;

FIG. 27 illustrates an exemplary circuit diagram for the power supplysystem shown in FIG. 26 shown in FIG. 26;

FIGS. 28A-28D illustrate simulation waveforms for the circuit diagramshown in FIG. 27;

FIG. 29 illustrates another exemplary circuit diagram for the powersupply system shown in FIG. 26 in which the power source for theauxiliary supply includes a capacitor;

FIGS. 30A-30E illustrate simulation waveforms for the circuit diagramshown in FIG. 29;

FIG. 31 illustrates another exemplary power supply system with theauxiliary switching converter moved inside the same package of loaddevice for fast responding to load transient conditions;

FIG. 32A illustrates another exemplary power supply system in which theoutput of the auxiliary switching converter is connected to the input ofthe main switching converter instead of to the load device to providethe holdup time when the main power source is temporary disconnected;

FIGS. 32B-32E illustrate waveforms of the power supply system shown inFIG. 32A in response to the input voltage source of the main powersource come temporary disconnected;

FIG. 33 illustrates an exemplary circuit diagram in which the output ofthe auxiliary supply is connected the input of the main supply to absorband reduce the input voltage ripple when there is a load transient;

FIG. 34A1-34A3 illustrate simulation waveforms of a conventional supplyhaving a large input voltage ripple caused by load transient;

FIG. 34B1-34B3 illustrate simulation waveform of a power supply systemshown in FIG. 33, which is configured to reduce the input voltage rippleduring load transient;

FIG. 35 illustrates another exemplary power supply system for whichcurrent or voltage transient is predictable by the load device or theapplication system.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant teachings. However, it should be apparent to those skilledin the art that the present teachings may be practiced without suchdetails. In other instances, well known methods, procedures, components,and/or circuit have been described at a relatively high-level, withoutdetail, in order to avoid unnecessarily obscuring aspects of the presentteachings.

There is a continuing search for a power supply system having a fastresponse to a transient condition at a load device with an improvedefficiency while reducing solution size and cost and increasing supplypower density. The load device may have different power requirements.This naturally means the power supply system may have to run asefficient as possible both to reduce size and to reduce input power tosave energy and increase efficiency. To this end, the power supplysystem may include a main switching converter and an auxiliary switchingconverter running in parallel with each other. The main switchingconverter may run at a first switching frequency and the auxiliaryswitching converter may run at a second switching frequency. The secondswitching frequency may be higher than the first switching frequency.Therefore, the main switching converter may have a higher efficiency(e.g., less power switching loss) than that of the auxiliary switchingconverter. In contrast, the auxiliary switching converter may have abetter transient performance (e.g., a faster transient response) thanthat of the main switching converter in response to a transient at theload device. Since the auxiliary switching converter may have a higherswitching loss than that of the main switching converter, the auxiliaryswitching converter may not be utilized to provide the main lowfrequency power to the load device during steady-state operation.Instead, the auxiliary switching converter may only be used to deal withthe transients to sink or source additional current with sudden increaseor decrease in the load current.

FIG. 1 illustrates an exemplary power supply system 100 configured tohave a fast transient response and a high efficiency. The power supplysystem 100 includes a power source 110, a load device 112, and a powerinterface device 114 coupled to the power source 110 and the load device112. The power source 110 is configured to output a certain standardvoltage. To this end, the power source 110 may be an electrical outlet.Most single phase alternating-current electrical outlets in the worldsupply power at 210-240 V or at 100-120 V. Alternatively, the powersource 110 may include other types of power sources such as, forexample, a battery, a solar photovoltaic, an AC generator, or a DCoutput voltage of a front-end power supply. Regardless of the type ofthe power source 110, usually the power source 110 provides a voltagedifferent than the required voltage for the load device 112. Theprovided voltage may be higher or lower than the required voltage forthe load device 112. To match the source voltage to the load voltage,the power supply system 100 includes the power interface device 114.

The power interface device 114 is configured to change the voltage ofthe power source 110 to an appropriate voltage for the load device 112.As noted above, the appropriate voltage for the load device 112 may behigher or lower than the voltage of the electrical power source 110. Inone implementation, the appropriate voltage for the load device 112 islower than the voltage of the electrical power source 110. In onespecific example, the power interface device 114 is configured to reducethe voltage of the electrical power source 110 from 12 volts to 1 voltfor the load device 112.

The load device 112 may include a resistive load, a magnetic load, acapacitive load, a heater, or modern electronic devices. Most modernelectronic devices require between 0.5 and 24 volts DC. These devicescan work either from batteries or mains. In either case, the powerinterface device 114 may be used to match the voltage requirements ofthese electronic devices with the voltage provided from the power source110. The power interface device 114 may be internal to the load device112 or may be external to the load device 112. Similarly, the powerinterface device 114 may be internal to the power source 110 or may beexternal to the power source 110.

The power interface device 114 may include a transformer, a rectifier,or switched-mode power supplies. The switched-mode power supplies havebecome widespread and are smaller and lighter because of their goodefficiency and high switching frequency. Additionally, becauseswitched-mode power supplies are typically rectified to operate at a DCvoltage, they are minimally affected by the frequency of the mains (50vs 60 Hz). The foregoing description assumes that power interface device114 includes switched-mode power supplies; however, as noted above, thepower interface device 114 may include circuits other than theswitched-mode power supplies.

The power interface device 114 includes two switched-mode powerconverters, a main switching converter 116 and an auxiliary switchingconverter 118. The main switching converter 116 may run in parallel tothe auxiliary switching converter 118 and at a lower switching frequency(fsw) for good efficiency and may source a lower frequency current tothe load device 112. The auxiliary switching converter 118 may run at ahigher switching frequency (fsw) to source fast transient higherfrequency current to the load device 112. Due to the higher switchingfrequency (fsw), the auxiliary switching converter 118 may be lessefficient or otherwise have more power loss than the main switchingconverter 116. Therefore, the auxiliary switching converter 118 may notbe used to handle the main low frequency power to the load device 112.To this end, the low frequency current of the auxiliary switchingconverter 118 should be minimized for good efficiency and low thermalstress. Instead, the auxiliary switching converter 118 may be used onlyto deal with the transients of the load device 112 to sink or sourceadditional current with sudden increase or decrease in the load current.

The power supply system 100 may have smaller size or be more efficientthan the previously discussed power supply system using only capacitorsor running only the main converter at a higher frequency. The powersupply system 100 can reduce the size of the capacitor needed on theoutput and as a result reduce supply size, PCB area and costs.

The switching converters 116 and 118 may be controlled in several ways.For example, the switching converters 116 and 118 may be controlled viaa non-linear control mechanism. Alternatively, the switching converters116 and 118 may be controlled via a linear control mechanism.

FIGS. 2A and 2B illustrate an exemplary power supply system 200including a main switching converter and an auxiliary switchingconverter. The power supply system 200 employs a non-linear controlmechanism for controlling the main switching converter and the auxiliaryswitching converter. The power supply system 200 includes a power source210, a load device 212, and a power interface device 214 coupled to thepower source 210 and the load device 212. The power source 210 and theload device 212 may be the same as the power source 110 and the loaddevice 112 described with respect to FIG. 1 and therefore they are notdescribed in more detail for brevity of description.

Similar to the power interface device 114, the power interface device214 includes a main switching converter 216 and an auxiliary switchingconverter 218. The main switching converter 216 may include a slowerswitching frequency (fsw) than that of the auxiliary switching converter218 and may be designed to work in steady-state operation. To this end,the main switching converter 216 may have good stability and low outputvoltage ripple, but consequently slow response to the transients at theload device 212. In contrast, the auxiliary switching converter 218 maybe configured to source or sink current to or from the output terminalonly during the transients. The main aim of the auxiliary switchingconverter 218 may be to provide a fast transient response by eithersinking or sourcing current to address decrease or increase of the loadcurrent. The power supply system 200 is described in more detail in anIEEE publication, titled “The Fast Response Double Buck DC-DC Converter(FRDB): Operation and Output Filter Influence” by Andres Barrado Vol.20, No. 6, November 2005, the content of which is incorporated herein byreference in its entirety.

FIG. 2B illustrates the exemplary components of the power supply system200 in more detail. As shown, two buck topologies are used to implementthe main switching converter 216 and the auxiliary switching converter218, and a resistive load is used for the load device 212. The powersupply system 200 may use a window comparator to detect if V_(out) isoutside of a regulation window. If so, the power supply system 200 turnson the auxiliary switching converter 218 to speed up transient response.If not, the power supply system 200 turns off the auxiliary switchingconverter 218 or maintains the auxiliary switching converter 218 in theoff condition. Although the power supply system 200 provides fastertransient response, the power supply system 200 requires an accuratewindow comparator, which is difficult to accomplish in practicalapplications if its V_(out) window needs to be tight and it can bepossibly falsely triggered by V_(out) noise/ripple. Additionally,non-linear control may cause large auxiliary inductor currentovershoot/undershoot and ringing.

FIGS. 3(A)-3(E) illustrate exemplary waveforms associated with the powersupply system 200 shown in FIGS. 2A-2B. Specifically, FIG. 3(A)illustrates a current load step in the load device 212 of the powersupply system 200. FIG. 3(B) illustrates output voltage of the powersupply 200 in response to the current load step of FIG. 3(A). As shown,in response to the load step of FIG. 3A, the voltage of capacitorreduces to supplement the inductor's slowly rising current to meet theincrease in current demand from the load device 212. Similarly, theoutput capacitor is useful in sinking the current to meet the suddendecrease in current from the load device 212. FIG. 3(C) illustrates dutycycle of the auxiliary switching converter 218. As shown, once theoutput voltage falls outside of the regulation window, the auxiliaryswitching converter 218 is enabled to either source or sink current tothe output with sudden increase or decrease in the load current. FIG.3(D) illustrates L/NL & E/D signal for selecting between the auxiliaryswitching converter and the main switching converter. As shown, when thevoltage falls outside of the regulation window, the L/NL & E/D signalenables the auxiliary switching converter 218 to either source or sinkcurrent to the output with sudden increase or decrease in the loadcurrent. FIG. 3(E) illustrates sourced or sunk current by the auxiliaryswitching converter 218 in response to sudden increase or decrease inthe load current.

FIG. 4 illustrates another exemplary power supply system 400 including amain switching converter and an auxiliary switching converter. The powersupply system 400 does not use non-linear control with V_(out) transientdetection as shown in FIG. 2. Instead, a linear control is used so itmay be easier to design and optimize the power supply system 400. Thepower supply system 400 also does not need an additional power capacitorfor separating the high frequency current from the low frequency currentfor driving the auxiliary switching converter. This can reduce the sizeand costs of the power supply system 400.

The power supply system 400 includes a power source 410, a load device412 and a power interface device 414 coupled to the power source 410 andthe load device 412. The power source 410 and the load device 412 aresimilar to the power source 110 and the load device 112. Therefore, forbrevity of description, they are not described in more detail. The powerinterface device 414 includes a main switching converter 416, anauxiliary switching converter 418, a feedback and compensation circuit420, a main control circuit 422, and an auxiliary control circuit 424.

The main switching converter 416 is connected in parallel with theauxiliary switching converter 418. The main switching converter 416 maybe configured to source or sink only a low frequency current. To thisend, the main switching converter 416 may be switching at a lowfrequency to maintain high efficiency of the main switching converter416. The auxiliary switching converter 418 may be configured to sourceor sink only a high frequency current. To this end, the auxiliaryswitching converter 418 may be switching at a high frequency to achievehigh loop bandwidth and track high frequency transient. In one specificexample, low and high are relative terms with respect to each other. Forexample, the low switching frequency may correspond to any switchingfrequency lower than the high switching frequency.

The main switching converter 416 may configured to sink and/or sourcecurrent both during the steady-state operation and the transient.Similarly, the auxiliary switching converter may operate both during thetransient and outside of the transient in the steady-state operation.During the transient, the auxiliary switching converter 418 may sourceor sink high frequency current to respond to the sudden increase ordecrease in the load current. During the steady-state condition, theauxiliary switching converter 418 may source or sink high frequencycurrent with a zero average or low frequency current to reduce powerloss associated with the auxiliary switching converter 418. In thismanner, in the steady-state condition, the power loss associated withthe low frequency current in the auxiliary switching converter 418 isreduced or eliminated and as such the total power loss in the auxiliaryswitching converter 418 is minimized. The auxiliary switching converter418, however, may still experience a little switching power loss due tothe switching of its switches in the steady-state condition.

The power interface device 414 also includes the feedback andcompensation circuit 420. The feedback and compensation circuit 420 isconnected at one end to the output terminal and at the other end to themain control circuit 422 and the auxiliary control circuit 424. Thefeedback and compensation circuit 420 is configured to detect transientsat the load device 412 and generate a transient signal for controllingthe switches in the main switching converter 416 and the auxiliaryswitching converter 418 based on the transient signal to provide astable V_(out) as quickly as possible.

The transient may include a scenario in which there is a sudden increaseor decrease in the load current or voltage. To illustrate one example,during a 25 A current load step at the output, the transient maycorrespond to the beginning of the load step, where there is a suddenincrease in the load current before reaching a first steady-state levelat the increased level of 25 A. Similarly, the transient may correspondto the ending of the load step where there is a sudden decrease in theload current before reaching a second steady-state level. The secondsteady-state may correspond to a state prior to the 25 A current loadstep or to a new state higher or lower than the state prior to the 25 Acurrent load step.

The transient signal is provided to the main control circuit 422 and theauxiliary control circuit 424. The transient signal includes a lowerfrequency component and a higher frequency component. The main controlcircuit 422 is configured to separate the lower frequency component ofthe transient signal from the total feedback compensation transientsignal and drive the main switching converter 416 based on the lowerfrequency component to respond to the transient condition. The auxiliarycontrol circuit 424 is configured to separate the higher frequencycomponent of the transient signal from the total feedback compensationtransient signal and drive the auxiliary switching converter 418 basedon the higher frequency component to respond to the transient condition.

To illustrate one specific example, if there is a sudden increase in theload current due to a positive current load step (e.g., from 75 A to 100A), the auxiliary control circuit 424 may drive the auxiliary switchingconverter 418 based on the higher frequency component of the transientsignal. Specifically, the auxiliary control circuit 424 may issue acontrol signal to the auxiliary switching converter 418 to source highfrequency current to the output terminal until the total output currentreaches the desired level of 100 A. In response, the auxiliary switchingconverter 418 may operate with an increased duty cycle and increase thesourced high frequency current to the output terminal until the totaloutput current reaches the desired level of 100 A. Due to its higherswitching frequency and higher loop bandwidth, the auxiliary switchingconverter 418 may source current faster to the output terminal from thepower source 410 than the main switching converter 416. The sourced highfrequency current from the auxiliary switching converter 418 may includenon-zero average low frequency (or DC) current and may track the higherfrequency component of the transient signal.

Once the current at the output terminal reaches the desired level (e.g.,100 A) and the load device 412 reaches the steady-state condition, theauxiliary switching converter 418 may reduce its duty cycle to theoriginal duty cycle. The auxiliary switching converter 418 may operatebased on the original duty cycle and may source a zero average lowfrequency (or DC) current output. To this end, a current or voltagethreshold level may be set for the auxiliary switching converter 418 inthe steady-state operation such that the average low frequency (or DC)current of the auxiliary switching converter 218 associated with thehigh frequency current ripple is zero. As such, the average sourcedcurrent from the auxiliary switching converter 418 may be non-zeroduring the transient and substantially zero outside the transient duringthe steady-state operation. That is, once the transient ends (e.g., thenew current threshold of 100 A is reached), the auxiliary switchingconverter 418 may sink or source substantially zero average lowfrequency (or DC) current.

In keeping with the previous example, if there is a sudden increase inthe load current due to the positive current load step (e.g., from 75 Ato 100 A), the main control circuit 422 may drive the main switchingconverter 416 based on the lower frequency component of the transientsignal. Specifically, the main control circuit 422 may issue a controlsignal to the main switching converter 416 to source current to theoutput terminal until the total output current reaches the desired levelof 100 A. In response, the main switching converter 416 may operate withan increased duty cycle and increase the sourced low frequency currentto the output terminal until the total output current reaches thedesired level of 100 A. The sourced current from the main switchingconverter 416 may track the lower frequency component of the transientsignal. Once the transient ends (e.g., the new current threshold of 100A is reached), the main switching converter 416 may continue to sourceand/or sink current to maintain the stability of V_(out) in accordancewith its fixed switching frequency and its original duty cycle. The dutycycle may be defined in accordance with Equation 1 below:D=V _(out) /V _(in)  (Equation 1)

To illustrate another specific example, if there is a sudden decrease inthe load current due to a negative current load step (e.g., from 100 Ato 75 A), the auxiliary control circuit 424 may operate the auxiliaryswitching converter 418 with a decreased duty cycle to increase sunkcurrent from the output terminal. Specifically, the auxiliary controlcircuit 424 may issue a control signal to the auxiliary switchingconverter 418 to sink current from the output terminal to the groundterminal until the total output current reaches the desired level of 75A. In response, the auxiliary switching converter 418 may operate with adecreased duty cycle and increase the sunk high frequency current fromthe output terminal until the total output current reaches the desiredlevel of 75 A. As mentioned above, due to its higher switching frequencyand higher loop bandwidth, the auxiliary switching converter 418 maysink current faster from the output terminal to the ground terminal thanthe main switching converter 416. The sunk current by the auxiliaryswitching converter 418 may track the higher frequency component of thetransient signal.

Once the current at the output terminal reaches the desired level (e.g.,75 A) and the load device 412 reaches the steady-state condition, theauxiliary switching converter 418 may increase its duty cycle to theoriginal duty cycle. The auxiliary switching converter 418 may operatebased on the original duty cycle and may source a zero average lowfrequency (or DC) current output. As such, the average sunk current fromthe auxiliary switching converter 418 may be non-zero during thetransient and substantially zero outside the transient during thesteady-state operation. That is, once the transient ends (e.g., the newcurrent threshold of 75 A is reached), the auxiliary switching converter418 may sink or source substantially zero average low frequency (or DC)current.

In keeping with the previous example, if there is a sudden decrease inthe load current due to the negative current load step (e.g., from 100 Ato 75 A), the main control circuit 422 may drive the main switchingconverter 416 based on the lower frequency component of the transientsignal. Specifically, the main control circuit 422 may issue a controlsignal to the main switching converter 416 to sink current from theoutput terminal until the total output current reaches the desired levelof 75 A. In response, the main switching converter 416 may operate witha decreased duty cycle and increase the sunk low frequency current fromthe output terminal until the total output current reaches the desiredlevel of 75 A. The sunk current may track the lower frequency componentof the transient signal. Once the transient ends (e.g., the new currentthreshold of 75 A is reached), the main switching converter 416 maycontinue to source and/or sink current to maintain the stability ofV_(out) in accordance with its fixed switching frequency and itsoriginal duty cycle as defined in Equation 1 above.

To separate the lower frequency component of the transient signal fromthe transient signal (e.g., the output of the feedback and compensationcircuit 420), the auxiliary control circuit 424 may employ a high passfilter. The high pass filter is configured to filter out the lowerfrequency component of the transient signal and allow the higherfrequency component of the transient signal to activate or drive theauxiliary switching converter 418. Similarly, the main control circuit422 may employ a low pass filter. The low pass filter is configured tofilter out the higher frequency component of the transient signal andallow the lower frequency current to activate or drive the mainswitching converter 416.

FIG. 5 illustrates another exemplary power supply system 500 including amain switching converter and an auxiliary switching converter. The powersupply system 500 is similar to the power supply system 400 with theexception the low pass filter (“LPF”) and the high pass filter (“HPF”)are shown to be included inside the power interface device 514 butoutside the main control circuit 522 and the auxiliary control circuit524, respectively. In contrast, in the power supply system 500, the LPFand the HPF were described to be inside the main control circuit 522 andthe auxiliary control circuit 524, respectively.

FIG. 6 illustrates an exemplary circuit diagram 600 of the power supplysystem 400 shown in FIG. 4 having a fast transient response. As shown,the power interface of the circuit diagram 600 includes a main switchingconverter 616, an auxiliary switching converter 618 connected inparallel with the main switching converter 616, a feedback andcompensation mechanism 620, a main control circuit 622, and an auxiliarycontrol circuit 624.

The main switching converter 616 corresponds to the main switchingconverter 416 and the auxiliary switching converter 618 corresponds tothe auxiliary switching converter 618. The main switching converter 616and the auxiliary switching converter 618 can be classified aspulse-width-modulation (PWM) type. The PWM produce a pulse train havinga constant frequency variable pulse width. The main switching converter616 is configured to run at a lower switching frequency fsw than that ofthe auxiliary switching converter 618. The auxiliary switching converter618 is configured to run at a higher switching frequency than that ofthe main switching regulator 616 to quickly respond to the transients atthe load device 612. Although the specific example shows two switchingconverters 616 and 618, the power interface device 600 may include morethan two switching converters. For example, the main switching converter616 can have two or more phases. Similarly, the auxiliary switchingconverter 618 can have two or more phases. To this end, the instantapplication is not limited to a single main switching converter 616 anda single auxiliary switching converter 618. Any number of suchconverters may be connected in parallel with each other.

The switching converters 616 and 618 may be current-mode switchingregulators that include an inductor. The switching converters 616 and618 may be synchronous switching regulators but they also may benon-synchronous switching regulators. In one specific example, theswitching converters 616 and 618 may be a step-down, current mode,switching regulators in which the input voltage V_(in) is greater thanthe output voltage V_(out). In another specific example, the switchingconverters 616 and 618 may be a step-up, current mode, switchingregulators in which the input voltage V_(in) is lower than the outputvoltage V_(out). In the foregoing and the following implementations, itis assumed that the switching converters 616 and 618 are a step-down,current mode, switching regulators.

The main switching converter 616 may include a first main switch 616 a,a second main switch 616 b, and a main inductor 616 c. The first mainswitch 616 a and the second main switch 616 b may be power FET switches.The power FET switches may be n-channel FET or p-channel FET switches.Similarly, the auxiliary switching converter 618 may include a firstauxiliary switch 618 a, a second auxiliary switch 618 b, and anauxiliary inductor 618 c. The first auxiliary switch 618 a and thesecond auxiliary switch 618 b may be power FET switches. The FETswitches may be n-channel FET or p-channel FET switches. Although FETtype switches are described, other appropriate technologies may also beused.

In the main switching converter 616, the first main switch 616 a may beconnected at one end to the V_(in) and at another end to a main node626. The second main switch 616 b may be connected at one end to themain node 626 and at the other end to the ground terminal. The maininductor 616 c may be connected at one end to the main node 626 and atthe other end to the output terminal 628. The output terminal 628 may beconnected to the output capacitor Cout and the load resistance R_(L).

In the auxiliary switching converter 618, the first auxiliary switch 618a may be connected at one end to V_(in) and at another end to anauxiliary node 630. The second auxiliary switch 618 b may be connectedat one end to the auxiliary node 630 and at the other end to the groundterminal. The auxiliary inductor 618 c may be connected at one end tothe auxiliary node 630 and at the other end to the output terminal 628.

The power interface device 600 is configured to source or sink outputcurrent to the load device 612 coupled to the output terminal 628 andmaintain a regulated voltage V_(out). To this end, the first main switch616 a and the second main switch 616 b in the main switching converter616 are switched ON and OFF by a main control circuit 622. The mainswitches 616 a and 616 b may be driven out of phase with respect to eachother to source or sink current to the load device 612 coupled to outputterminal 628. Similarly, the first auxiliary switch 618 a and the secondauxiliary switch 618 b in the auxiliary switching regulator 618 areswitched ON and OFF by an auxiliary control circuit 624. The auxiliaryswitches 618 a and 618 b may be driven out of phase with respect to eachother to source or sink current to the load device 612 coupled to outputterminal 628.

The main switching converter 616 is configured to run at a firstswitching frequency. The auxiliary switching converter 618 is configuredto run at a second switching frequency. The second switching frequencymay be higher than the first switching frequency. The higher secondswitching frequency may allow the auxiliary switching converter 618 torespond to the transients at the load device 612 more quickly than themain switching converter 616. That is, due to the faster switchingfrequency, the auxiliary switching converter 618 is configured to sourceor sink current to or from the load device 612 more quickly than themain switching converter 616. Due to the higher switching frequency, theauxiliary switching converter 618 may have more power loss than the mainswitching converter 616. To reduce this power loss, the operation of theauxiliary switching converter 618 may be limited to the transientconditions experienced by the load device 612. That is, the auxiliaryswitching converter 618 may only source or sink current during thetransients and may provide zero load current during the steady-stateoperation.

Although not shown, additional circuit may be added to the powerinterface device 600 to provide a brief dead-time or blanking intervalbetween the moment that one switching transistor turns OFF and themoment that the other switching transistor turns ON. When the switches616 a, 618 a are ON and the switches 616 b, 618 b are OFF, current flowsfrom the V_(in) to the output terminal 628 through the inductors 616 c,618 c in each of the single phase switching regulators 616 and 618. Inthis scenario, the rate of change of inductor current 616 c and 618 cover time may be equal to (V_(in)−V_(out))/L. When the switches 616 a,618 a are OFF and the switches 616 b, 618 b are ON, current flows fromthe ground terminal to output terminal 628 though the inductors 616 cand 618 c. In this scenario, the rate of change of inductor currents 616c and 618 c over time may be equal to −V_(out)/L. In each of theabove-described scenarios, the total current at the output terminal maybe the cumulative inductor currents through inductors 616 c and 618 c.

The power interface device 600 also includes the feedback andcompensation mechanism 620. The feedback and compensation mechanism 620is connected at one end to the output terminal 628 and at the other endto the control circuits 622, 624. The feedback and compensationmechanism 620 is configured to detect transient conditions and controlthe switches in the single phase switching regulators 616 and 618 toprovide a stable V_(out) as quickly as possible. To this end, thefeedback and compensation mechanism 620 includes a feedback voltagesense circuit, an error amplifier 620 a, and a compensation circuit 620b.

The feedback voltage sense circuit is configured to sense the V_(out)through a network of resistors and capacitors including R₁, R₂, C₁, andC₂. The network of resistors R₁ and R₂ form a resistor divider and scalethe signal V_(out) to make it proportional to a reference voltageV_(ref). The reference voltage V_(ref) may correspond to the desiredoutput voltage. The optional capacitors C₁ and C₂ may be provided tomake the resistor divider frequency dependent. This frequency dependentdivided V_(out) may be referred to as feedback voltage V_(fb). Thefeedback voltage V_(fb) and the reference voltage V_(ref) are providedas input to the error amplifier gm (shown as a trans-conductance (gm)amplifier) 620 a. The error amplifier 620 a may be either acurrent-output type transconductance amplifier or a voltage-output typeamplifier. In one specific example, the error amplifier 620 a is acurrent-output type transconductance amplifier.

The error amplifier 620 a monitors the feedback voltage V_(fb) that isproportional to V_(out) at its inverting input and a reference voltageV_(ref) at its non-inverting input. The feedback voltage V_(fb) shouldbe approximately equal to the reference voltage V_(ref). When these twovoltages are not equal, the error amplifier 620 a may provide atransient signal ITH at its output. The transient signal ITH may includea higher frequency component ITH_(AC) and a lower frequency componentITH_(DC).

In keeping with the previous example, the error amplifier 620 a may be acurrent-output type transconductance amplifier and may output thetransient current signal ITH. In this scenario, when the feedbackvoltage V_(fb) is not proportional to the reference voltage V_(ref), theerror amplifier 620 a may source current to its output terminal toenable either increase or decrease of the output voltage to match thereference voltage V_(ref). When the feedback voltage V_(fb) issubstantially proportional to the reference voltage V_(ref), the erroramplifier 620 a may source substantially zero current to its outputterminal to enable maintaining of the output voltage at its currentlevel.

In another example, the error amplifier 620 a may be a voltage-outputtype amplifier and may output a transient voltage signal ITH. In thisscenario, when the feedback voltage V_(fb) is not proportional to thereference voltage V_(ref), the error amplifier 620 a may source avoltage to its output terminal to enable either increase or decrease ofthe output voltage to match the reference voltage V_(ref). When thefeedback voltage V_(fb) is substantially proportional to the referencevoltage V_(ref), the error amplifier 620 a may source substantially zerovoltage to its output terminal to enable maintaining of the outputvoltage at its current level.

The voltage output from the amplifier 620 a may correspond to thedifference between the actual output voltage and the desired outputvoltage. The output voltage of the error amplifier 620 a is inverse tothe feedback voltage V_(fb). As the feedback voltage V_(fb) decreases,the output voltage of the error amplifier 620 a increases. As thefeedback voltage V_(fb) increases, the output voltage of error amplifier620 a decreases.

The frequency compensation circuit 620 b includes capacitors C_(th) andC_(thp) and a resistor R_(th) to provide frequency compensation for thefeedback loop. The capacitor C_(thp) is connected at one end to anoutput of the error amplifier 620 a and at another end to the groundterminal. The capacitor C_(th) is connected at one end to the output ofthe amplifier 620 a and at another end to the resistor R_(th). Theresistor R_(th) at one end is connected to the capacitor C_(th) and atanother end to the ground terminal. The frequency compensation circuit620 b is configured to receive the transient signal ITH and output afrequency compensated transient signal ITH to the main control circuit622 and the auxiliary control circuit 624.

The main control circuit 622 includes a main buffer 622 a, a low passfilter 622 b, and a main comparator 622 c. The main buffer 622 a may beconfigured to provide electrical impedance transformation from thefeedback and compensation mechanism 620 to the main control circuit 622.The main buffer 622 a may be a voltage buffer or a current buffer. Thetype of the buffer may be selected to correspond to the type of theerror amplifier 620 a. The main buffer 622 a includes an input terminaland an output terminal. The input terminal of the main buffer 622 a iscoupled to the output terminal of the amplifier 620 a. The outputterminal of the main buffer 622 a is coupled to the low pass filter 622b.

The low pass filter 622 b is configured to block the higher frequencycomponent ITH_(AC) of the transient signal ITH and allow the lowerfrequency component ITH_(DC) of the transient signal ITH to passthrough. The low pass filter 622 b includes a resistor and a capacitor.The resistor at one end is connected to the output of the main buffer622 a and at another end is connected to a first node. The capacitor atone end is connected to the first node and at another end is connectedto the ground terminal.

The main comparator 622 c includes a non-inverting terminal, aninverting terminal, and an output terminal. The non-inverting terminalis connected to the first node and configured to receive the lowerfrequency component ITH_(DC). The inverting terminal is connected to themain inductor 616 c and is configured to receive the sensed maininductor 616 c signal. The sensed main inductor 616 c signal may be asensed current i_(LDC) in the main inductor 616 c (low frequencyinductor current). The main comparator 622 c is configured to comparethe lower frequency component ITH_(DC) with the sensed current i_(LDC)and generate a main control signal for main power FETs 616 a and 616 b.The main control signal may be a PWM control signal.

If the lower frequency component ITH_(DC) is more than the sensed maininductor signal, the main comparator 622 c may output a first maincontrol signal. In one implementation, the lower frequency componentITH_(DC) and the sensed main inductor signal may be both a voltagesignal. In another implementation, the lower frequency componentITH_(DC) and the sensed main inductor signal may be both a currentsignal.

The first main control signal may be a high signal. The high signal maybe provided to the first main switch 616 a to turn ON the first mainswitch 616 a and enable the main switching converter 616 to sourceadditional current to the output terminal 628 with the increased loadcurrent. The high signal may also be provided to an invertor connectedto the second main switch 616 b to turn OFF the second main switch 616b. At the beginning of the clock cycle, the first main switch 616 a mayturn ON with an increased duty cycle until the new current threshold dueto the transient is reached. During the time the first main switch 616 ais ON, the low frequency current flows from the power source V_(in)through the first main switch 616 a and the main inductor 616 c to theoutput terminal 628. As a result, the low frequency current ramps up inthe main inductor 616 c toward the new current threshold.

In this manner, the main switching converter 616 sources low frequencycurrent tracking the lower frequency component ITH_(DC) to reach the newcurrent threshold set by the transient. In one implementation, duringthe transient, the first main switch 616 a may remain ON and the secondmain switch 616 b may remain OFF until the new current threshold set bythe transient is reached. In another implementation, during thetransient, the main switching converter 616 may operate with anincreased duty cycle to increase the sourced low frequency current tothe output terminal 628. During the increased duty cycle and in responseto the first main control signal, the main switches 616 a and 616 b mayalternatively turn ON and OFF to increase the sourced low frequencycurrent to the output terminal 628. The increased duty cycle maycorrespond to the duty cycle of the first main signal. The fixedswitching frequency of the main switching converter 616 may not bemaintained during the transient if the on-time for the first main switch616 a is longer than the cycle time T, for example.

If the lower frequency component ITH_(DC) is less than the sensed maininductor signal, the main comparator 622 c may output a second maincontrol signal. The second main control signal may be a low signal. Thelow signal may be provided to the first main switch 616 a to turn OFFthe first main switch 616 a. The second main control signal may also beprovided to the invertor connected to the second main switch 616 b toturn ON the second main switch 616 b and enable the main switchingconverter 616 to sink additional current from the output terminal 628with the decreased load current. At the beginning of the clock cycle,the first main switch 616 a may turn OFF and the second main switch 616b may turn ON until the new current threshold due to the transient isreached. During the time the second main switch 616 b is ON, the lowfrequency current flows from the output terminal 628 though the maininductor 616 c to the ground terminal. As a result, the low frequencycurrent ramps down in the main inductor 616 c toward the new currentthreshold.

In this manner, the main switching converter 616 sinks low frequencycurrent tracking the lower frequency component ITH_(DC) to reach the newcurrent threshold set by the transient. In one implementation, duringthe transient, the first main switch 616 a may remain OFF and the secondmain switch 616 b may remain ON until the new current threshold set bythe transient is reached. In another implementation, during thetransient, the main switching converter 616 may operate with a decreasedduty cycle to increase the sunk low frequency current from the outputterminal 628. During the decreased duty cycle and in response to the lowsignal, the main switches 616 a and 616 b may alternatively turn ON andOFF to increase the sunk low frequency current from the output terminal628. In either case, the fixed switching frequency of the main switchingconverter 616 may not be maintained during the transient if the on-timefor the second main switch 616 b is longer than the cycle time T, forexample.

Once the transient ends (e.g., the new current threshold is reached),the main switching converter 616 continues to source and sink current tomaintain the stability of V_(out) in accordance with its fixed switchingfrequency and a duty cycle. The on-time and the off-time of the mainswitches 616 a and 616 b are determined based on the duty-cycle. In onespecific example, the duty-cycle may correspond to the duty-cycle setprior to the transient and is identified above in Equation 1. To thisend, the main switching converter 616 is configured to source and/orsink current both during the transient and steady-state operation.

As noted above, the total output transient signal ITH of the erroramplifier 620 b is also passed to the auxiliary control circuit 624. Theauxiliary control circuit 624 includes an auxiliary buffer 624 a, a highpass filter 624 b, and an auxiliary comparator 624 c. The auxiliarybuffer 624 a may be configured to provide electrical impedancetransformation from the feedback and compensation mechanism 620 to theauxiliary control circuit 624. The auxiliary buffer 624 a may be avoltage buffer or a current buffer. The type of buffer may be selectedbased on the type of the error amplifier 620 a. The auxiliary buffer 624a may include an input terminal and an output terminal. At the inputterminal, the auxiliary buffer 624 a is connected to the output of theerror amplifier 620 a. At the output terminal, the auxiliary buffer 624a is connected to the high pass filter 624 b.

The high pass filter 624 b is configured to block the lower frequencycomponent ITH_(DC) and allow the higher frequency component ITH_(AC) ofthe transient signal ITH to pass through. The high pass filter 624 bincludes a resistor and a capacitor. The capacitor at one end isconnected to the output of the auxiliary buffer 624 a and at another endis connected to a second node. The resistor at one end is connected tothe second node and at another end is connected to the ground terminal.

The auxiliary comparator 624 c includes a non-inverting terminal, aninverting terminal, and an output terminal. The non-inverting terminalis connected to the second node and configured to receive the higherfrequency component ITH_(AC). The inverting terminal is connected to theauxiliary inductor 618 c and is configured to receive the sensedauxiliary inductor 618 c signal. The sensed auxiliary inductor 618 csignal may include sensed current i_(LAC) in the auxiliary inductor 618c (high frequency inductor current). The auxiliary comparator 624 c isconfigured to compare the higher frequency component ITH_(AC) with thesensed current i_(LAC) and generate an auxiliary control signal forauxiliary switches 618 a and 618 b. The auxiliary control signal mayinclude a PWM pulse train.

If the higher frequency component ITH_(AC) is more than the sensedauxiliary inductor signal, the auxiliary comparator 624 c may output afirst auxiliary control signal. The first auxiliary control signal maybe a high signal. In one implementation, the higher frequency componentITH_(AC) and the sensed auxiliary inductor signal may be both a voltagesignal. In another implementation, the higher frequency componentITH_(AC) and the sensed auxiliary inductor signal may be both a currentsignal.

The high signal may be provided to the first auxiliary switch 618 a toturn ON the first auxiliary switch 618 a and enable the auxiliaryswitching converter 618 to source additional current to the outputterminal 628 with the increased load current. The high signal may alsobe provided to an invertor connected to the second auxiliary switch 618b to turn OFF the second auxiliary switch 618 b. At the beginning of theclock cycle, the first auxiliary switch 618 a may turn ON with anincreased duty cycle until the new current threshold due to thetransient is reached. During the time the first auxiliary switch 618 ais ON, the high frequency current flows from the power source V_(in)through the first auxiliary switch 618 a and the auxiliary inductor 618c to the output terminal 628. As a result, the high frequency currentramps up in the auxiliary inductor 618 c toward the new currentthreshold.

In this manner, the auxiliary switching converter 618 sources highfrequency current tracking the higher frequency component ITH_(AC) toreach the new current threshold set by the transient. In oneimplementation, during the transient, the first auxiliary switch 618 amay remain ON and the second auxiliary switch 618 b may remain OFF untilthe new current threshold set by the transient is reached. In anotherimplementation, during the transient, the auxiliary switching converter618 may operate with an increased duty cycle to increase the sourcedhigh frequency current to the output terminal 628. During the increasedduty cycle and in response to the high signal, the auxiliary switches618 a and 618 b may alternatively turn ON and OFF to increase thesourced high frequency current to the output terminal 628. The increasedduty cycle may correspond to the duty cycle of the first auxiliarycontrol signal. The fixed switching frequency of the auxiliary switchingconverter 618 may not be maintained during the transient if the on-timefor the first auxiliary switch 618 a is longer than the cycle time T,for example.

If the higher frequency component ITH_(AC) is less than the sensedauxiliary inductor signal, the auxiliary comparator 624 c may output asecond auxiliary control signal. The second auxiliary control signal isa low signal. The low signal may be provided to the first auxiliaryswitch 618 a to turn OFF the first auxiliary switch 618 a. The lowsignal may also be provided to the invertor connected to the secondauxiliary switch 618 b to turn ON the second auxiliary switch 618 b andenable the auxiliary switching converter 618 to sink additional currentfrom the output terminal 628 with the decreased load current. At thebeginning of the clock cycle, the first auxiliary switch 618 a may turnOFF and the second auxiliary switch 618 b may turn ON until the newcurrent threshold due to the transient is reached. During the time thesecond auxiliary switch 618 b is ON, the high frequency current flowsfrom the output terminal 628 though the auxiliary inductor 618 c to theground terminal. As a result, the high frequency current ramps down inthe auxiliary inductor 618 c toward the new current threshold.

In this manner, the auxiliary switching converter 618 sinks highfrequency current tracking the higher frequency component ITH_(AC) toreach the new current threshold set by the transient. In oneimplementation, during the transient, the first auxiliary switch 618 amay remain OFF and the second auxiliary switch 618 b may remain ON untilthe new current threshold set by the transient is reached. In anotherimplementation, during the transient, the auxiliary switching converter618 may operate with a decreased duty cycle to increase the sunk highfrequency current from the output terminal 628. During the decreasedduty cycle and in response to the second auxiliary control signal, theauxiliary switches 618 a and 618 b may alternatively turn ON and OFF toincrease the sunk high frequency current from the output terminal 628.In either case, the fixed switching frequency of the auxiliary switchingconverter 618 may not be maintained during the transient if the on-timefor the second auxiliary switch 618 b is longer than the cycle time T,for example.

Once the transient ends (e.g., the new current threshold is reached),the auxiliary switching converter 618 continues to operate but maysource or sink substantially zero average low frequency (or DC) current.In this manner, the power loss due to the high switching frequency ofthe auxiliary switching converter 618 may be limited substantially toits operation during the transient and not outside of the transient.

If the main switching converter 616 is a peak-current mode regulator,first the second main switch 616 b may be turned OFF and then the firstmain switch 616 a may be turned ON by an internal clock or timer,thereby increasing the current i_(LDC) of the main inductor 616 c.Similarly, if the auxiliary switching converter 618 is a peak-currentmode regulator, first the second auxiliary switch 618 b may be turnedOFF and then the first auxiliary switch 618 a may be turned ON by aninternal clock or timer, thereby increasing the current i_(LAC) of theauxiliary inductor 618 c.

If the main switching converter 616 is a valley-current mode regulator,first the first main switch 616 a is turned OFF and then the second mainswitch 616 b is turned ON by the internal clock or timer, therebydecreasing the current i_(LDC) of the main inductor 616 c. Similarly, ifthe auxiliary switching converter 618 is a valley-current moderegulator, first the first auxiliary switch 618 a is turned OFF and thenthe second auxiliary switch 618 b is turned ON by the internal clock ortimer, thereby decreasing the current i_(LAC) of the auxiliary inductor618 c.

Although a single first main switch 616 a and a second main switch 616 bare shown in the main switching converter 616, other implementations arepossible. For example, the number of first main (high side) switches maybe two or more. Similarly, the number of second main (low side) switchesmay be two or more. To this end, the control circuit may simultaneouslyenable more than one high side switch depending on the signal from thedriver circuit 622. Similarly, the control circuit may simultaneouslyenable more than one low side switch depending on the signal from thedriver circuit 622.

FIG. 7 illustrates an exemplary simulation circuit diagram 700 for thecontrol mechanism of the power supply system 600 shown in FIG. 6. Thecircuit diagram 700 includes a feedback and compensation mechanism 720,a main control circuit 722, and an auxiliary control circuit 724. Thefeedback and compensation mechanism 720 corresponds to the feedback andcompensation mechanism 620; the main control circuit 722 corresponds tothe main control circuit 622; and the auxiliary control circuit 724corresponds to the auxiliary control circuit 624. Therefore, they arenot described further for brevity of description.

FIGS. 8A-8C illustrate exemplary load transient simulation waveforms forthe circuit diagram 600 shown in FIG. 6. FIG. 8A illustrates thetransient signal ITH 810, the higher frequency component ITH_(AC) 814 ofthe transient signal ITH 810, and the lower frequency component ITH_(DC)812 of the transient signal ITH 810. As shown, the transient signal ITH810 is a summation of the higher frequency component ITH_(AC) 814 andthe lower frequency component ITH_(DC) 812.

The higher frequency component ITH_(AC) 814 has voltage overshoot orundershoot only during the sudden increase or decrease in the outputcurrent. In this case, the higher frequency component ITH_(AC) 814 isonly present during the positive edge and the negative edge of the loadstep shown in FIG. 8B. The lower frequency component ITH_(DC) 812 mayalso be changed at a slower speed during the sudden increase or decreasein the output current. However, once the new current threshold isreached due to the transient, the lower frequency component of currentin steady state may follow the lower frequency component ITH_(DC) 812.As such, the lower frequency component ITH_(DC) 812 is not shown to fadeaway after the transient ends. To this end, the higher frequencycomponent ITH_(AC) 814 may rise quickly in response to positive edge ofthe load step shown in FIG. 8B and then falls. In contrast, the lowerfrequency component ITH_(DC) 812 may raise slowly in response to thepositive edge of the load step shown in FIG. 8B and once it reaches aspecific threshold level, it may remain there for the duration of theload step. Similarly, the higher frequency component ITH_(AC) 814 mayfall quickly in response to negative edge of the load step shown in FIG.8B. In contrast, the lower frequency component ITH_(DC) 812 may fallslowly in response to the negative edge of the load step shown in FIG.8B.

FIG. 8B illustrates a current load step 816 and the corresponding outputvoltage 818 in response to the current load step 816. As shown, theoutput voltage 818 declines with the positive edge of the load step 816and rises with a negative edge of the load step 816. The reason for thisis because the voltage of capacitor reduces to supplement the inductor'sslowly rising current to meet the increase in current demand from theload device. Similarly, the output capacitor is useful in sinking thecurrent to meet the sudden decrease in current from the load device.Therefore, as shown, there is a slight voltage ripple at the output.However, this voltage ripple may be significantly reduced compared tothe voltage ripple of the conventional power supply system not employingthe teachings of the instant application. In one specific example, theoutput voltage ripple may be reduced by approximately 50%. This may beaccomplished without a need for a complicated control method oremploying an additional AC capacitor between the output terminal and thecontrol loop for the auxiliary switching converter. The AC capacitor isconfigured to prevent DC or low frequency current from entering thecontrol loop for auxiliary switching converter. The AC capacitor can addto the cost and size of the power supply system. Instead, the powersupply system of the instant application as described with respect toFIG. 4 may prevent the DC or low frequency current from entering theauxiliary switching converter via a filtering network that is configuredto filter out the lower frequency component of the transient signal ITH.

FIG. 8C illustrates a lower frequency inductor iL_(DC) current 820provided by the main switching converter in response to the lowerfrequency component ITH_(DC) 812 and a higher frequency inductor iL_(AC)current 822 provided by the auxiliary switching converter in response tothe higher frequency component ITH_(AC) 814. As shown, the higherfrequency current 822 tracks the higher frequency component ITH_(AC) 814and the lower frequency current 820 tracks the lower frequency componentITH_(DC) 812 in transient state and also tracks the lower frequencycurrent in steady state operation. To this end, the auxiliary switchingconverter may only source or sink current during the transients (e.g.,sourcing current in response to the positive edge of the load step andsinking current in response to the negative edge of the load step). Incontrast, the main switching converter may source or sink current bothduring the transient and the steady state operation.

FIG. 9A illustrates a loop gain comparison between a first power supplysystem including two phase buck switching converters and a second powersupply system including two phase buck switching converters in parallelwith an auxiliary switching converter. As can be seen, with the additionof the auxiliary switching converter, the bandwidth of the second powersupply system can be pushed from 80 kHz to 1 MHz, making a fastertransient response possible. Usually the power supply system is stablewhen phase margin is greater than zero. In one implementation, it may bedesirable to have 40-45 degrees phase.

FIG. 9B illustrates phase margin for the first power supply system andthe second power supply system of FIG. 9A. As can be seen the phasemargin of the first power supply system using only two phase buckswitching converters at 100 kHz is about 40 degrees. In contrast, thephase margin of the second power supply system is substantially higher,higher than 60 degrees at 100 kHz.

FIG. 10 illustrates another exemplary power supply system 1000 includinga main switching converter and an auxiliary switching converter. Thepower supply system 1000 is similar to the power supply system 500except it includes an optional error amplifier 1010 to further ensurethat the higher frequency inductor iL_(AC) current generated by theauxiliary switching converter has zero average current in steady state.To this end, the additional error amplifier 1010 receives the averagehigh frequency current iL_(AC) sourced from the auxiliary switchingconverter at its inverting terminal and the 0 A Tref at itsnon-inverting terminal. The error amplifier output provides an offsetsignal to current comparator 1012 to form a slow loop and ensureinductor iL_(AC) current has 0 A DC average value. The comparator 1012also receives the sensed current iL_(AC) and the higher frequencycomponent of the transient signal ITH. The higher frequency component ofthe transient signal ITH is added to the offset signal and compared withthe sensed current iL_(AC). The comparator 1012 uses these input togenerate an auxiliary control signal for driving the auxiliary switchingconverter.

In another implementation, the power supply system may include twoseparate and independent control mechanisms. The two separateindependent control mechanisms may include a first control mechanism fordriving a main switching converter and a second and separate controlmechanism for driving the auxiliary switching converter. This design maybe useful if the main switching converter is part of a power module,which does not provide an interconnection pin to share its controlmechanism with the auxiliary switching converter to enable a fastertransient response. To enable the faster transient response, anauxiliary power interface device may be combined with this power modulewithout changing the main switching converter. The auxiliary powerinterface device may include an auxiliary control mechanism and anauxiliary switching converter. The auxiliary control mechanism isconfigured to receive the sensed V_(out) and the low frequency averageV_(out) signal generated through a low pass filter, and detect thehigher frequency compensation component of the V_(out) and run theauxiliary switching converter based on the higher frequency compensationcomponent of the V_(out).

FIG. 11 illustrates an exemplary circuit diagram 1100 including twoindependent control mechanisms of the instant application. The twoindependent control mechanisms include a main switching convertercontrol mechanism 1110 and an auxiliary switching converter controlmechanism 1120. The main switching converter control mechanism 1110 maybe part of a power module that does not provide an interconnection forsharing the main switching control mechanism 1110 with an auxiliaryswitching converter.

The main switching converter control mechanism 1110 includes a mainfeedback voltage sense circuit 1112, a main error amplifier 1114, a maincompensation circuit 1116, and a main control circuit 1118. The mainfeedback voltage sense circuit 1112 is connected at one end to theV_(out) and at the other end to the main error amplifier 1114. The mainfeedback voltage sense circuit 1112 is configured to sense the V_(out)through a network of resistors and capacitors including R1, R2, C1, andC2. The network of resistors R1 and R2 form a resistor divider and scalethe signal V_(out) to make it proportional to V_(ref). The optionalcapacitors C1 and C2 are provided to make the divider frequencydependent. This frequency dependent divided V_(out) may be referred toas feedback voltage V_(fb). The feedback voltage V_(fb) and a referencevoltage V_(ref) are input to the main error amplifier gm (shown as atrans-conductance (gm) amplifier) 1114. The main error amplifier 1114may be either a current-output type transconductance amplifier orvoltage-output type amplifier.

The main error amplifier 1114 monitors the feedback voltage V_(fb) thatis proportional to V_(out) at its inverting input and a referencevoltage V_(ref) at its non-inverting input. The feedback voltage V_(fb)should be approximately equal to the reference voltage V_(ref). Whenthese two voltages are substantially not equal, the main error amplifier1114 may provide a transient signal at its output. The main frequencycompensation circuit 1116 includes capacitors and resistors to providefrequency compensation for the feedback loop. The main frequencycompensation circuit 1116 may attenuate the higher frequency componentof the transient signal and output the lower frequency transient signal.The lower frequency transient signal is provided to the main controlcircuit 1118.

The main control circuit 1118 includes a comparator. The comparatorreceives at its inverting input the sensed current i_(LDC) in theinductor of the main switching converter and at its non-inverting inputthe lower frequency component of the transient signal. The lowerfrequency component of the transient signal is compared with the sensedcurrent i_(LDC) in the inductor (low frequency inductor current) togenerate the main control signal for driving the main switchingconverter.

The auxiliary switching converter control mechanism 1120 includes anauxiliary feedback sense circuit, an auxiliary error amplifier 1124, anauxiliary compensation circuit 1126, an auxiliary buffer, a high passfilter (“HPF”), and an auxiliary control circuit 1128. The auxiliaryfeedback sense circuit at one end is connected to the V_(out) and atanother end is connected to the auxiliary error amplifier 1124. Theauxiliary feedback sense circuit includes a low pass filter. The lowpass filter is configured to output the lower frequency average V_(out)signal. The sensed V_(out) is directly coupled to the inverting terminalof the auxiliary error amplifier 1124 and the lower frequency averageV_(out) signal is coupled to the non-inverting terminal of the auxiliaryerror amplifier 1124.

The sensed V_(out) should be approximately equal to its lower frequencyaverage V_(out) signal during the steady-state operation. When these twovoltages are not equal during a transient event, the auxiliary erroramplifier 1124 may provide a higher frequency compensation component ofthe V_(out) at its output. The auxiliary frequency compensation circuit1126 includes capacitors and resistors to provide frequency compensationfor the feedback loop. The auxiliary frequency compensation circuit 1126may enhance the higher frequency compensation component of the V_(out)and output the higher frequency compensation component of the V_(out) tothe auxiliary buffer and then to the HPF. The auxiliary buffer may beconfigured to provide electrical impedance transformation from theauxiliary compensation circuit 1126 to the auxiliary control circuit1128. The higher frequency compensation component of the V_(out) maythen pass through the HPF to ensure it does not contain a lowerfrequency compensation component before being provided to the auxiliarycontrol circuit 1128. The higher frequency compensation component of theV_(out) is then provided to the non-inverting terminal of the auxiliarycomparator and compared with the sensed current i_(LAC) in the inductor(high frequency inductor current) of the auxiliary switching converterto generate an auxiliary control signal for driving the auxiliaryswitching converter.

In one specific example, V_(in) may be 12V, V_(out) may be 1V, thecurrent load step may be 25 A, the switching frequency of the mainswitching converter may be 500 kHz, the switching frequency of theauxiliary switching converter may be 5 MHz, the inductance of theinductors in the main switching converter may be 220 nH, and theinductance of the inductor in the auxiliary switching converter may be20 nH.

FIG. 12 illustrates another exemplary circuit diagram 1200 for thecontrol loop of the power supply system 600 shown in FIG. 6. The circuitdiagram 1200 includes a feedback and compensation mechanism 1220, a maincontrol circuit 1222 and an auxiliary control circuit 1224. The feedbackand compensation mechanism 1220 is similar to the feedback andcompensation circuit 720 described with respect to FIG. 7. The controlcircuits 1222 and 1224 are similar to the control circuits 722 and 724described with respect to FIG. 7 except they do not include their ownbuffer and instead share a common buffer 1226. The common buffer 1226 isconfigured to connect the feedback and compensation mechanism 1220 tothe control circuits 1222 and 1224. As such, the circuit diagram 1200has fewer components than the circuit diagram 700.

The common buffer 1226 is commonly shared by the main control circuit1222 and the auxiliary control circuit 1224 and configured to isolatethe main control circuit 1222 and the auxiliary control circuit 1224from an impedance of the feedback and compensation circuit 1220. Thecommon buffer 1226 at one end is connected to the output of theamplifier in the feedback and compensation circuit 1220 and at anotherend is connected to the main control circuit 1222 and the auxiliarycontrol circuit 1224.

The main control circuit 1222 includes a low pass filter and acomparator. The low pass filter includes a resistor and a capacitor. Theresistor at one end is connected to the output of the common buffer 1226and at another end is connected to a first node. The capacitor at oneend is connected to the first node and at another end is connected tothe ground terminal. The comparator includes a non-inverting terminal,an inverting terminal, and an output terminal. The non-invertingterminal is connected to the first node and configured to receive thelower frequency component ITH_(DC). The inverting terminal is connectedto the inductor 616 c and is configured to receive the sensed currenti_(LDC) in the inductor 616 c (low frequency inductor current). Thecomparator is configured to compare the lower frequency componentITH_(DC) with the sensed current i_(LDC) and generate the main controlsignal for power FETs 616 a and 616 b.

The auxiliary control circuit 1224 includes a high pass filter and acomparator. The high pass filter includes a resistor and a capacitor.The capacitor at one end is connected to the output of the common buffer1226 and at another end is connected to a second node. The resistor atone end is connected to the second node and at another end is connectedto the ground terminal. The comparator includes a non-invertingterminal, an inverting terminal, and an output terminal. Thenon-inverting terminal is connected to the second node and configured toreceive the higher frequency component ITH_(AC). The inverting terminalis connected to the inductor 618 c and is configured to receive thesensed current i_(LAC) in the inductor 618 c (high frequency inductorcurrent). The comparator is configured to compare the higher frequencycomponent ITH_(AC) with the sensed current i_(LAC) and generate theauxiliary control signal for power FETs 618 a and 618 b.

FIGS. 13A-13C illustrate exemplary load transient simulation waveformsfor the power supply system 600 controlled by the control mechanismshown in FIG. 12. FIG. 13A illustrates the transient voltage signal ITH1310, the higher frequency component ITH_(AC) 1314 of the transientvoltage signal ITH 1310, and the lower frequency component ITH_(DC) 1312of the transient voltage signal ITH 1310. As shown, the transientvoltage signal ITH 1310 is a summation of the higher frequency componentITH_(AC) 1314 and the lower frequency component ITH_(DC) 1312. As shown,the higher frequency component ITH_(AC) 1314 has a sharp rise inresponse to the positive edge of the current load step shown in FIG. 13Cand then it slowly falls. Similarly, the higher frequency componentITH_(AC) 1314 has a sharp fall in response to the negative edge of thecurrent load step shown in FIG. 13C and then it slowly rises. Incontrast, the lower frequency component ITH_(DC) 1312 has a slow rise inresponse to the positive edge of the current load step shown in FIG. 13Cand once it hits a given threshold level, it remains at that giventhreshold level for the duration of the current load step shown in FIG.13C. Once the current load step terminates and in response to thenegative edge of the current load step shown in FIG. 13C, the lowerfrequency component ITH_(DC) 1312 slowly declines to a new thresholdlevel. As such, the lower frequency component ITH_(DC) 1312 is not shownto fade away after the transient ends.

FIG. 13B illustrates low frequency regulator inductor current waveform1316 and high frequency regulator inductor current waveform 1318 duringtransients in the power supply system 600 shown in FIG. 6 and controlledby the control mechanism shown in FIG. 12. As shown, the low frequencyregulator inductor current waveform 1316 tracks the lower frequencycomponent ITH_(DC) 1312, and the high frequency regulator inductorcurrent waveform 1318 tracks the higher frequency component. ITH_(AC)1314.

FIG. 13C illustrates output voltage overshoot 1320 a and undershoot 1320b for a load step 1322 in the power supply system 600 shown in FIG. 6and controlled by the control mechanism shown in FIG. 12. As shown, thevoltage overshoot and undershoot for the circuit 1200 is minimized inresponse to the transient.

FIG. 14A illustrates another exemplary power supply system 1400Aincluding two separate control signals for driving the main switchingconverter and the auxiliary switching converter. The power supply system1400A includes a power source 1410, a load device 1412, and a powerinterface 1414 coupled to the power source 1410 and the load device1412. The power source 1410 and the load device 1412 are similar to thepower source 110 and the load device 112 shown in FIG. 1 and thereforefor brevity are not described.

The power interface 1414 is similar to the power interface 514 with theexception that the power supply system 1400 employs only a low passfilter (LPF) for filtering out the higher frequency component of thetransient signal instead of the high pass filter. To illustrate, thepower interface 1414 includes a main switching converter 1416, anauxiliary switching converter 1418, a feedback and compensation circuit1420, a main control circuit 1422, an auxiliary control circuit 1424, aLPF 1426, and an adder circuit 1428.

The main control circuit 1422 is coupled to the feedback andcompensation circuit and the main switching converter 1416. The maincontrol circuit 1422 is configured to receive the transient signal fromthe feedback and compensation circuit 1420 and to generate a maincontrol signal based on the transient signal for driving the mainswitching converter 1416. In response to the main control signal, themain switching converter 1416 either sources or sinks current to theload device 1412. The current may be low frequency current due to thelow switching frequency of the main switching converter 1416.

The main control circuit 1422 is configured to directly receive thetransient signal from the feedback and compensation mechanism 1420. Tothis end and unlike the main control circuit 522, the main controlcircuit 1422 does not employ a low pass filter. Instead, to reduce theimpact of the higher frequency component of the transient signal on themain switching converter 1416, the feedback and compensation circuit1420 may output a transient signal with an attenuated higher frequencycomponent. The transient signal is directly received by the maincomparator inside the main control circuit 1422. The main comparator isconfigured to receive the transient signal from the feedback andcompensation mechanism 1420 at its non-inverting terminal and the sensedlow frequency inductor voltage sourced by the main switching converter1416 at its inverting terminal and generate the main control signal.

The low pass filter 1426 at one end is coupled to the feedback andcompensation circuit 1420 and at another end is coupled to the addercircuit 1428. The low pass filter 1426 is configured to receive thetransient signal from the feedback and compensation circuit 1420 andoutput a lower frequency component of the transient signal to the addercircuit 1428. The adder circuit 1428 is coupled to the low pass filter1426 and the feedback and compensation circuit 1420.

The adder circuit 1428 is configured to receive the lower frequencycomponent of the transient signal from the low pass filter 1426 at itsinverting terminal and the transient signal from the feedback andcompensation circuit 1420 at its non-inverting terminal, subtract thelower frequency component of the transient signal from the transientsignal, and output the higher frequency component of the transientsignal to the auxiliary control circuit 1424. In addition, the adder mayalso have an amplify gain K to enhance its output of the higherfrequency component of transient signal.

The auxiliary control circuit 1424 is coupled to the adder circuit 1428and the auxiliary switching converter 1418. The auxiliary controlcircuit 1424 is configured to receive the higher frequency component ofthe transient signal and generate an auxiliary control signal based onthe higher frequency component for driving the auxiliary switchingconverter 1418. In response to the auxiliary control signal, theauxiliary switching converter 1418 either sources or sinks current tothe load device 1412. The current may be high frequency current due tothe high switching frequency of the auxiliary switching converter 1418.However, the current may only be sourced or sunk during the transientand not in steady state. In the steady state, the average current outputfrom the auxiliary switching converter 1418 may be substantially zero.

The auxiliary control circuit 1424 may include an auxiliary comparator.The auxiliary comparator is configured to receive the higher frequencycomponent of the transient signal from the adder circuit 1428 at itsnon-inverting terminal and the sensed high frequency inductor voltagesourced by the auxiliary switching converter 1418 at its invertingterminal and generate the auxiliary control signal.

FIG. 14B illustrates another exemplary power supply system 1400Bincluding two separate control signals for driving the main switchingconverter and the auxiliary switching converter. The power supply system1400B is similar to the power supply system 1400A except the powersupply system 1400B utilizes a high pass filter (HPF) instead a low passfilter.

To this end, the power supply system 1400B includes a main switchingconverter 1416, an auxiliary switching converter 1418, a feedback andcompensation circuit 1420, a main control circuit 1422, an auxiliarycontrol circuit 1424, a HPF 1430, and an adder circuit 1432. The mainswitching converter 1416, auxiliary switching converter 1418, feedbackand compensation circuit 1420, main control circuit 1422, and auxiliarycontrol circuit 1424 are similar to those described with respect to FIG.14A and are not described further. The HPF 1430 and the adder circuit1432 are described further below.

The HPF 1430 is coupled to the feedback and compensation circuit 1420,the auxiliary control circuit 1424, and the adder circuit 1432. The HPFis configured to receive the transient signal from the feedback andcompensation circuit 1420 and output a higher frequency component of thetransient signal. The higher frequency component of the transient signalis provided to the auxiliary control circuit 1424. The auxiliary controlcircuit 1424 is configured to generate an auxiliary control signal basedon the higher frequency component of the transient signal for drivingthe auxiliary switching converter 1418. The higher frequency componentis also supplied to the adder circuit 1432.

The adder circuit 1432 is coupled to HPF 1430, the feedback andcompensation circuit 1420, and the main control circuit 1422. The addercircuit 1432 is configured to receive the higher frequency component ofthe transient signal from the HPF 1430 and the transient signal from thefeedback and compensation circuit 1420 and output a lower frequencycomponent of the transient signal to the main control circuit 1422. Themain control circuit 1422 is configured to generate a main controlsignal based on the lower frequency component of the transient signalfor driving the main switching converter 1416.

The adder circuit 1432 is configured to receive the higher frequencycomponent of the transient signal from the HPF 1430 at its invertingterminal and the transient signal from the feedback and compensationcircuit 1420 at its non-inverting terminal, subtract the higherfrequency component of the transient signal from the transient signal,and output the lower frequency component of the transient signal to themain control circuit 1422.

Referring again to FIG. 14A, in another implementation, the LPF 1426 maybe placed between node 1450 and the main control circuit 1422. In thismanner, the transient signal is passed through the LPF 1426 to provide alower frequency component of the transient signal to the main controlcircuit 1422. The lower frequency component of the transient signal alsogoes the inverting input of the adder circuit 1428. The adder circuit1428 receives the transient signal on its non-inverting input andoutputs the amplified higher frequency component of the transient signalto the auxiliary control circuit 1424 for controlling the auxiliaryswitching converter 1418. The amplification of the higher frequencycomponent of the transient signal may increase the bandwidth and theresponse time of the auxiliary switching converter 1418 to the transientcondition.

FIG. 15 illustrates an exemplary circuit diagram 1500 for the powersupply system 1400A shown in FIG. 14A having a fast transient response.As shown, the circuit diagram 1500 includes a power source 1510, a loaddevice 1512, and a power interface device 1514 connecting the powersource 1510 to the load device 1512. The power interface device 1514includes a plurality of main switching converters 1516 and an auxiliaryswitching converter 1518 connected in parallel with each other. Thepower interface device 1514 also includes a feedback and compensationcircuit 1530, a main control circuit 1532, an auxiliary control circuit1534, and a high pass filter 1536.

The main switching converter 1516 and the auxiliary switching converter1518 can be classified as pulse-width-modulation (PWM) type, producing apulse train having a fixed frequency and a variable pulse width. Themain switching converter 1516 is configured to run at a lower switchingfrequency fsw than that of the auxiliary switching converter 1518. Theauxiliary switching regulator 1518 is configured to run at a higherfrequency than that of the main switching regulator 1516 to quicklyrespond to the transients at the load device 1512. Although the specificexample shows four main switching converters 1516 and a single auxiliaryswitching converter 1518, the power supply system 1500 may include moreor less than four main switching converters 1516 and more than oneauxiliary switching converter 1518. Any number of such regulators may beconnected in parallel with each other.

The switching converters 1516 and 1518 may be current-mode switchingregulators that include an inductor. The switching converters 1516 and1518 may be synchronous switching regulators but they also may benon-synchronous switching regulators. In one specific example, theswitching converters 1516 and 1518 may be a step-down, current mode,switching regulator in which the input voltage V_(in) is greater thanthe output voltage V_(out).

Each of the main switching converters 1516 may include a first mainswitch 1516 a, a second main switch 1516 b, and a main inductor 1516 c.The first main switch 1516 a and the second main switch 1516 b may bepower FET switches. The power FET switches may be n-channel FET orp-channel FET switches. Similarly, the auxiliary switching converter1518 may include a first auxiliary switch 1518 a, a second auxiliaryswitch 1518 b, and an auxiliary inductor 1518 c. The first auxiliaryswitch 1518 a and the auxiliary second switch 1518 b may be power FETswitches. The FET switches may be n-channel FET or p-channel FETswitches. Although FET type switches are described, other appropriatetechnologies may also be used.

In the main switching converter 1516, the first main switch 1516 a maybe connected at one end to the V_(in) and at another end to a main node1520. The second main switch 1516 b may be connected at one end to themain node 1520 and at the other end to the ground terminal. The maininductor 1516 c may be connected at one end to the main node 1520 and atthe other end to the output terminal 1522. The output terminal 1522 maybe connected to the output capacitor C_(out) and the load resistanceR_(L).

In the auxiliary switching regulator 1518, the first auxiliary switch1518 a may be connected at one end to V_(in) and at another end to anauxiliary node 1524. The second auxiliary switch 1518 b may be connectedat one end to the auxiliary node 1524 and at the other end to the groundterminal. The auxiliary inductor 1518 c may be connected at one end tothe auxiliary node 1524 and at the other end to the output terminal1528.

The power interface device 1514 is configured to source or sink outputcurrent to the load device 1512 coupled to the output terminal 1522 tomaintain a regulated voltage V_(out) at the output terminal 1522. Tothis end, the first main switch 1516 a and the second main switch 1516 bin the main switching converter 1516 are switched ON and OFF by the maincontrol circuit 1532. The switches 1516 a and 1516 b may be driven outof phase with respect to each other to source or sink current to theload device 1512 coupled to output terminal 1522. Similarly, the firstauxiliary switch 1518 a and the second auxiliary switch 1518 b in theauxiliary switching regulator 1518 are switched ON and OFF by anauxiliary control circuit 1534. The switches 1518 a and 1518 b may bedriven out of phase with respect to each other to source or sink currentto the load device 1512 coupled to output terminal 1522.

The main switches 1516 a and 1516 b are configured to run at a firstswitching frequency. The auxiliary switches 1518 a and 1518 b areconfigured to run at a second switching frequency. The second switchingfrequency may be higher than the first switching frequency to respond tothe transients at the output terminal 1522 more quickly. That is, due tothe faster switching frequency, the auxiliary switching converter 1518is configured to source or sink current to or from the output terminal1522 more quickly than the main switching converter 1516. Due to thehigher frequency, the auxiliary switching converter 1518 may have morepower loss than the main switching converter 1516. To reduce the powerloss associated with the auxiliary switching converter 1518, theoperation of the auxiliary switching converter 1518 may be controlledsuch that in the steady-state operation, the auxiliary switchingconverter 1518 provides substantially zero low frequency (or DC) currentto the output terminal 1522 as discussed above.

Although not shown, additional circuit may be added to the powerinterface device 1514 to provide a brief dead-time or blanking intervalbetween the moment that one switching transistor turns OFF and themoment that the other switching transistor turns ON. When the switches1516 a, 1518 a are ON and the switches 1516 b, 1518 b are OFF, currentflows from the V_(in) to the output terminal 1522 through the inductors1516 c, 1518 c in each of the switching converters 1516 and 1518. Inthis scenario, the rate of change of inductor current 1516 c and 1518 cover time may be equal to (V_(in)−V_(out))/L. When the switches 1516 a,1518 a are OFF and the switches 1516 b, 1518 b are ON, current flowsfrom the ground terminal to output terminal 1522 though the inductors1516 c and 1518 c. In this scenario, the rate of change of inductorcurrents 1516 c and 1518 c over time may be equal to −V_(out)/L. In eachof the above-described scenarios, the total current at the outputterminal 1522 may be the cumulative inductor currents through inductors1516 c and 1518 c.

The power interface device 1514 also includes the feedback andcompensation mechanism 1530. The feedback and compensation mechanism1530 is connected at one end to the output terminal 1522 and at theother end to the main control circuit 1532 and the auxiliary controlcircuit 1534. In one implementation, a low pass filter may be connectedin between the feedback and compensation mechanism 1530 and the maincontrol circuit 1532. The low pass filter is configured to filter outthe higher frequency component of the transient signal ITH and providethe main control circuits 1532 with only the low frequency component ofthe transient signal. In another implementation, the components of thecompensation circuit may be selected such that the transient signal ITHhas an attenuated higher frequency component such that it can bedirectly supplied to the main control circuits 1532 as shown in FIG. 15.

The feedback and compensation circuit 1530 includes a feedback sensecircuit 1530 a, an error amplifier 1530 b, and a compensation circuit1530 c. The feedback sense circuit 1530 a is configured to sense theV_(out) through a network of resistors R₁ and R₂. The network ofresistors R₁ and R₂ form a resistor divider and scale the signal V_(out)to make it proportional to V_(ref). In one implementation, the resistorR₁ is equal to 4.16 kilohms and R₂ is equal to 10 kilohms.

Although not shown, the feedback sense circuit 1530 a may also include anetwork of capacitors C₁ and C₂. The optional capacitors C₁ and C₂ maybe provided to make the resistor divider frequency dependent. Thisfrequency dependent divided V_(out) may be referred to as feedbackvoltage V_(fb). The feedback voltage V_(fb) and a reference voltageV_(ref) are provided as input to the error amplifier gm (shown as atrans-conductance (gm) amplifier) 1530 b. In one implementation, thereference voltage V_(ref) may correspond to the regulated output voltageIn one specific example, the reference voltage V_(ref) is equal to 0.6volt. The error amplifier 1530 b may be either a current-output typetransconductance amplifier or voltage-output type amplifier.

The error amplifier 1530 b monitors the feedback voltage V_(fb) that isproportional to V_(out) at its inverting input and a reference voltageV_(ref) at its non-inverting input. The feedback voltage V_(fb) shouldbe approximately equal to the reference voltage V_(ref). When these twovoltages are not substantially equal, the error amplifier 1530 b mayprovide a transient signal ITH at its output. As described before,depending on the type of the error amplifier 1530 b, the error amplifier1530 b may output a transient voltage signal ITH or a transient currentsignal ITH. In the following examples, it is assumed that the erroramplifier 1530 b outputs a transient voltage signal ITH.

The output voltage of the error amplifier 1530 b may correspond to thedifference between the actual output voltage and the desired outputvoltage. The output voltage of the error amplifier 1530 b is inverse tothe feedback voltage V_(fb). As the feedback voltage V_(fb) decreases,the output voltage of the error amplifier 1530 b increases. As thefeedback voltage V_(fb) increases, the output voltage of error amplifier1530 b decreases. The frequency compensation circuit 1530 c includescapacitors C_(th) and C_(thp) and a resistor R_(th) to provide frequencycompensation for the feedback loop. In one implementation, C_(th) isequal to 1.5 nF, C_(thp) is equal to 100 pF, and resistor R_(th) isequal to 10 kilohms. In the current-mode supply system, instead ofvoltage, the error amplifier 1530 b may provide transient current signalat its output. In either case, the transient signal (current or voltage)is used to control the total output current of converters 1516 and 1518.

The main control circuit 1532 includes a main resistor 1532 a and a maincomparator 1532 c. The main control circuit 1532 may also include a mainbuffer. The main buffer may be configured to provide electricalimpedance transformation from the feedback and compensation mechanism1530 to the main control circuit 1532. The main buffer may be a voltagebuffer or a current buffer. The type of the main buffer may be selectedbased on the type of the error amplifier 1530 b. The main comparator1532 c is configured to receive at its non-inverting input either thetransient signal ITH or the lower frequency component ITH_(DC) of thetransient signal ITH and compare it with the sensed voltage i_(L)*R_(i)(low frequency current of inductor 1516 c*resistance Ri) to generate themain control signal for power FETs 1516 a and 1516 b. The main resistorR_(i) is provided to sense the main inductor 316 c current and generatethe corresponding voltage for comparison with the lower frequencycomponent ITH_(DC) of the transient signal ITH.

If the lower frequency component ITH_(DC) is more than the sensedinductor voltage signal, the main comparator 1532 b may output a firstmain control signal. The first main control signal may be a high signal.The high signal may be provided to the first main switch 1516 a to turnON the first main switch 1516 a and enable the main switching converter1516 to source additional current to the output terminal 1522 with theincreased load current. The high signal may also be provided to aninvertor connected to the second main switch 1516 b to turn OFF the mainswitch 1516 b. At the beginning of the clock cycle, the first mainswitch 1516 a may turn ON with an increased duty cycle until the newcurrent threshold due to the transient is reached. During the time thefirst main switch 1516 a is ON, the current flows from the power sourceV_(in) through the first main switch 1516 a and the main inductor 1516 cto the output terminal 1522. Due to the low switching frequency of themain switching converter 1516, the output current is a low frequencycurrent. As a result, the low frequency current ramps up in the inductor1516 c toward the new current threshold.

In this manner, the main switching converter 1516 sources low frequencycurrent tracking the lower frequency component ITH_(DC) to reach the newcurrent threshold set by the transient. In one implementation, duringthe transient, the first main switch 1516 a may remain ON and the secondmain switch 1516 b may remain OFF until the new current threshold set bythe transient is reached. In another implementation, during thetransient, the main switching converter 1516 may operate with anincreased duty cycle to increase the sourced low frequency current tothe output terminal 1522. During the increased duty cycle and inresponse to the main control signal, the main switches 1516 a and 1516 bmay alternatively turn ON and OFF to increase the sourced low frequencycurrent to the output terminal 1522. The increased duty cycle maycorrespond to the duty cycle of the main control signal. The fixedswitching frequency of the main switching converter 1516 may not bemaintained during the transient if the on-time for the first main switch1516 a is longer than the cycle time T, for example.

In one implementation, the main control circuit 1532 may activate onlyone of the main switching converters 1516 to source the necessarycurrent to the output terminal 1522. In another implementation, the maincontrol circuit 1532 may activate more than one of the main switchingconverters 1516 to source the necessary current to the output terminal1522.

If the lower frequency component ITH_(DC) is less than the sensedinductor signal, the main comparator 1532 b may output a second maincontrol signal. The second main control signal is a low signal. The lowsignal may be provided to the first main switch 1516 a to turn OFF thefirst main switch 1516 a. The low signal may also be provided to theinvertor connected to the second main switch 1516 b to turn ON thesecond main switch 1516 b and enable the main switching converter 1516to sink additional current from the output terminal 1522 with thedecreased load current. At the beginning of the clock cycle, the firstmain switch 1516 a may turn OFF with a decreased duty cycle and thesecond main switch 1516 b may turn ON until the new current thresholddue to the transient is reached. During the time the second main switch1516 b is ON, the low frequency current flows from the output terminal1522 though the main inductor 1516 c to the ground terminal. As aresult, the low frequency current ramps down in the main inductor 1516 ctoward the new current threshold.

In this manner, the main switching converter 1516 sinks low frequencycurrent tracking the lower frequency component ITH_(DC) to reach the newcurrent threshold set by the transient. In one implementation, duringthe transient, the first main switch 1516 a may remain OFF and thesecond main switch 1516 b may remain ON until the new current thresholdset by the transient is reached. In another implementation, during thetransient, the main switching converter 1516 may operate with adecreased duty cycle to increase the sunk low frequency current from theoutput terminal 1522. During the decreased duty cycle and in response tothe second main control signal, the main switches 1516 a and 1516 b mayalternatively turn ON and OFF to increase the sunk low frequency currentfrom the output terminal 1522. In either case, the fixed switchingfrequency of the main switching converter 1516 may not be maintainedduring the transient if the on-time for the second main switch 1516 b islonger than the cycle time T, for example.

Once the transient ends (e.g., the new current threshold is reached),the main switching converter 1516 continues to source and sink currentto maintain the stability of V_(out) in accordance with its fixedswitching frequency and a duty cycle. The on-time and the off-time ofmain switches 1516 a and 1516 b are determined based on the duty-cycle.In one specific example, the duty-cycle may correspond to the duty-cycleset prior to the transient. To this end, the main switching converter1516 is configured to source and/or sink current both during thetransient and steady-state operation.

As noted above, the total transient signal ITH output from the feedbackand compensation circuit 1530 is also passed to the auxiliary controlcircuit 1534 via the high pass filter 1536. The high pass filter 1536includes a buffer 1536 a, a low pass filter 1536 b, resistors 1536 c and1536 d, an offset voltage 1536 e, a resistor 1536 f, an amplifier 1536g, and a resistor 1536 h. The buffer 1536 a is configured to isolate theauxiliary control circuit 1534 from the impedance of the feedback andcompensation network 1530. The output of the buffer 1536 a is suppliedto the non-inverting terminal of the amplifier 1536 g through theresistor 1536 d. The output of the buffer 1536 a is also supplied to theinverting terminal of the amplifier 1536 g through the low pass filter1536 b and the resistor 1536 c. The low pass filter 1536 b includes aresistor R_(f) and a capacitor C_(f) and is configured to filter out thehigher frequency component ITH_(AC) of the transient signal ITH andforward the lower frequency component ITH_(DC) of the transient signalITH to the inverting terminal of the amplifier 1536 g via the resistor1536 c. In one specific example, the resistance of the resistor R_(f) isequal to 1 kilohms and the capacitance of the capacitor C_(f) is equalto 1 nF.

The lower frequency component ITH_(DC) is subtracted from the transientsignal ITH (having both the higher frequency and lower frequencycomponents) and the difference is amplified by a K factor. As such, theoutput of the amplifier 1536 g may correspond to the amplified higherfrequency component ITH_(AC) of the transient signal ITH. The amplifiedhigher frequency component ITH_(AC) is supplied to the auxiliary controlcircuit 1534.

In one implementation, the resistors 1536 c, 1536 d, 1536 f, and 1536 hcombined together provide a gain factor for the higher frequencycomponent ITH_(AC) of the transient signal ITH. In one specific example,the resistance of the resistors 1536 c, 1536 d, 1536 f, and 1536 h isequal to 10 kilohms. The factor K may be equal to 30.

The V_(offset) 1536 e may be provided so that during the steady-stateoperation, the low frequency (or DC) current of the auxiliary switchingconverter 1518 is substantially zero. To this end, the V_(offset) 1536 emay be set to a value corresponding to half ripple of the high frequency(or AC) current such that during the steady-state operation averageripple AC current is substantially equal to zero. In one specificexample, the V_(offset) 1536 e is set to 100 millivolt.

The auxiliary control circuit 1534 includes an auxiliary resistor 1534 aand an auxiliary comparator 1534 b. The auxiliary resistor 1534 a isprovided to sense the auxiliary inductor 1518 c current and provide thesensed auxiliary inductor 1518 c voltage. The auxiliary comparator 1534b is configured to receive at its non-inverting terminal the amplifiedhigher frequency component ITH_(AC) and at its inverting terminal thesensed auxiliary inductor 1518 c voltage. The auxiliary comparator 1534b compares the higher frequency component ITH_(AC) with the sensedauxiliary inductor 1518 c voltage.

If the higher frequency component ITH_(AC) is more than the sensedauxiliary inductor signal, the comparator 1534 b may output a firstauxiliary control signal. The first auxiliary signal may be a highsignal. The high signal may be provided to the first auxiliary switch1518 a to turn ON the first auxiliary switch 1518 a and enable theauxiliary switching converter 1518 to source additional current to theoutput terminal 1522 with the increased load current. The high signalmay also be provided to an invertor connected to the second auxiliaryswitch 1518 b to turn OFF the second auxiliary switch 1518 b. At thebeginning of the clock cycle, the first auxiliary switch 1518 a may turnON with an increased duty cycle until the new current threshold due tothe transient is reached. During the time the first auxiliary switch1518 a is ON, the high frequency current flows from the power sourceV_(in) through the first auxiliary switch 1518 a and auxiliary inductor1518 c to the output terminal 1522. As a result, the high frequencycurrent ramps up in the auxiliary inductor 318 c toward the new currentthreshold.

In this manner, the auxiliary switching converter 1518 sources highfrequency current tracking the higher frequency component ITH_(AC) toreach the new current threshold set by the transient. In oneimplementation, during the transient, the first auxiliary switch 1518 amay remain ON and the second auxiliary switch 1518 b may remain OFFuntil the new current threshold set by the transient is reached. Inanother implementation, during the transient, the auxiliary switchingconverter 1518 may operate with an increased duty cycle to increase thesourced high frequency current to the output terminal 1522. During theincreased duty cycle and in response to the first auxiliary controlsignal, the auxiliary switches 1518 a and 1518 b may alternatively turnON and OFF to increase the sourced high frequency current to the outputterminal 1522. The increased duty cycle may correspond to the duty cycleof the first auxiliary control signal. The fixed switching frequency ofthe auxiliary switching converter 1518 may not be maintained during thetransient if the on-time for the first auxiliary switch 1518 a is longerthan the cycle time T, for example. Once the steady-state is reached,the auxiliary switching converter 1518 may source and sink highfrequency current with substantially zero average low frequency (or DC)current to the load device 1512.

If the higher frequency component ITH_(AC) is less than the sensedauxiliary inductor current signal, the auxiliary comparator 1534 b mayoutput a second auxiliary control signal. The second auxiliary controlsignal is a low signal. The low signal may be provided to the firstauxiliary switch 1518 a to turn OFF the first auxiliary switch 1518 a.The low signal may also be provided to the invertor connected to thesecond auxiliary switch 1518 b to turn ON the second auxiliary switch1518 b and enable the auxiliary switching converter 1518 to sinkadditional current from the output terminal 1522 with the decreased loadcurrent. At the beginning of the clock cycle, the first auxiliary switch1518 a may turn OFF with a decreased duty cycle and the second auxiliaryswitch 1518 b may turn ON until the new current threshold due to thetransient is reached. During the time the first auxiliary switch 1518 bis ON, the high frequency current flows from the output terminal 1522though the auxiliary inductor 1518 c to the ground terminal. As aresult, the high frequency current ramps down in the auxiliary inductor1518 c toward the new current threshold.

In this manner, the auxiliary switching converter 1518 sinks highfrequency current tracking the higher frequency component ITH_(AC) toreach the new current threshold set by the transient. In oneimplementation, during the transient, the first auxiliary switch 1518 amay remain OFF and the second auxiliary switch 1518 b may remain ONuntil the new current threshold set by the transient is reached. Inanother implementation, during the transient, the auxiliary switchingconverter 1518 may operate with a decreased duty cycle to increase thesunk high frequency current from the output terminal 1522. During thedecreased duty cycle and in response to the second auxiliary controlsignal, the auxiliary switches 1518 a and 1518 b may alternatively turnON and OFF to increase the sunk high frequency current from the outputterminal 1522. In either case, the fixed switching frequency of theauxiliary switching converter 1518 may not be maintained during thetransient if the on-time for the second auxiliary switch 1518 b islonger than the cycle time T, for example.

The control signals from the main control circuit 1532 and the auxiliarycontrol circuit 1534 may be provided to a control circuit internal tothe main switching converter 1516 and auxiliary switching converter1518, respectively. The control circuit uses the main control signal ofthe main control circuit 1532 along with a system clock signal tocontrol the state of main switches 1516 a and 1516 b of the mainswitching converter 1516. Similarly, the control circuit uses theauxiliary control signal of the auxiliary control circuit 1534 alongwith the system clock signal to control the state of auxiliary switches1518 a and 1518 b of the auxiliary switching converter 1518.

If the main switching converter 1516 is a peak-current mode regulator,first its second (low-side) main switch 1516 b may be turned OFF andthen its first (high-side) main switch 1516 a may be turned ON byinternal clock, thereby increasing the current of the main inductor 1516c. Similarly, if the auxiliary switching converter 1518 is apeak-current mode regulator, first its first (low-side) auxiliary switch1518 b may be turned OFF and then its second (high-side) auxiliaryswitch 1518 a may be turned ON by internal clock, thereby increasing thecurrent of the auxiliary inductor 1518 c.

If the main switching converter 1516 is a valley-current mode regulator,first the first (high-side) main switch 1516 a is turned OFF and thenthe second (low-side) main switch 1516 b is turned ON by internal clockor timer, thereby decreasing the current of the main inductor 1516 c.Similarly, if the auxiliary switching converter 1518 is a valley-currentmode regulator, first the first (high-side) auxiliary switch 1518 a isturned OFF and then the second (low-side) auxiliary switch 1518 b isturned ON by internal clock or timer, thereby decreasing the current ofthe inductor 1518 c.

FIG. 16A illustrates an exemplary simulation circuit diagram 1600 forthe power system 1500 shown in FIG. 15 with following values:

Power Supply V_(in)=12V

Output Voltage V_(out)=1V

Number of Main Switching Converter Phase=1

Number of Auxiliary Switching Converter Phase=1

Switching Frequency of Main Switching Converters F_(sw-DC)=400 kHz

Switching Frequency of Auxiliary Switching Converter F_(sw-AC)=2 MHz

Inductance of Main Switching Converter=330 nH (per phase)

Inductance of Auxiliary Switching Converter=75 nH

Output Capacitance Co=3*330 μF+2*100 μF

In FIG. 16A, the circuit diagram 1600 includes a power source 1610, aload device 1612, and a power interface 1614. The power interface 1614includes a main switching converter 1616 and an auxiliary switchingconverter 1618. The main switching converter 1616 includes a maincontroller 1617, a first main switch Q1, a second main switch Q2, and amain inductor L1. The main controller 1617 may be an LTC3866, producedby Linear Technology Corp. The LTC3866 is a single phase current modesynchronous step-down switching regulator controller that drives allN-channel power MOSFET switches.

The first main switch Q1 is connected to the power source 1610 at itsdrain terminal, a main node 1630 at its source terminal, and to the TGpin of the main controller 1617 at its gate terminal. The second mainswitch Q2 is connected to the main node 1630 at its drain terminal, aground terminal at its source terminal, and to the BG pin of the maincontroller 1617 at its gate terminal. The main node 1630 is connected tothe SW pin of the main controller 1617 and to the main inductor L1. Themain inductor L1 at one end is connected to the main node 1630 and atanother end is connected to the load device 1612 at the output terminal.

The auxiliary switching converter 1618 includes an auxiliary controller1619, a first auxiliary switch Q4, a second auxiliary switch Q3, and anauxiliary inductor L2. The auxiliary controller 1619 may be LTC3833,produced by Linear Technology Corp. The LTC 3833 is a synchronousstep-down DC/DC switching regulator controller targeted for high powerapplications. The controlled on-time valley current mode architectureallows for both fast transient response and constant frequency switchingin steady-state operation, independent of VIN, VOUT and load current.

The first auxiliary switch Q4 is connected to the power source 1610 atits drain terminal, an auxiliary node 1640 at its source terminal, andto the TG pin of the auxiliary controller 1619 at its gate terminal. Thesecond auxiliary switch Q3 is connected to the auxiliary node 1640 atits drain terminal, a ground terminal at its source terminal, and to theBG pin of the auxiliary controller 1619 at its gate terminal. Theauxiliary node 1640 is connected to the SW pin of the auxiliarycontroller 1619 and to the auxiliary inductor L2. The auxiliary inductorL2 at one end is connected to the auxiliary node 1640 and at another endis connected to the load device 1612 at the output terminal through asense resistor Rsense1.

The circuit diagram 1600 also includes a feedback sense circuit 1620, anerror amplifier, a compensation circuit 1622, a high pass filter 1624.The feedback sense circuit 1620 includes resistors R4 and R5. Theresistor R4 at one end is connected to the output terminal through theDIFFOut pin of the main controller 1617 and at another end is connectedto a node 1632. The resistor R5 at one is connected to the node 1632 andat another end is connected to the ground terminal. The node 1632provides the feedback voltage V_(fb) that is proportional to a referencevoltage V_(ref). The reference voltage V_(ref) may correspond to thedesired voltage at the output terminal. The feedback voltage is providedto the FB pin of the main controller 1617, which in turn may be providedto the error amplifier. The error amplifier compares the feedbackvoltage V_(fb) with the reference voltage V_(ref) and if they are notsubstantially equal to each other may output a transient signal ITH.

In one implementation, the error amplifier may be placed inside the maincontroller 1617. In another implementation, the error amplifier may beplaced outside of the main controller 1617. The output transient signalITH may be connected to the ITH pin of the main controller 1617. The ITHpin may in turn be connected to the feedback compensation circuit 1622.The feedback compensation circuit 1622 may be configured to providefrequency compensation for the feedback loop. As shown, in one specificexample, the feedback compensation circuit 1622 includes a capacitor C2and C13 and a resistor R17. The capacitor C2 at one end is connected tothe ground terminal and at another end is connected to the resistor R17.The resistor R17 at one end is connected to the capacitor C2 and atanother end is connected to the ITH pin of the main controller 1617. Thecapacitor C13 at one end is connected in parallel with the capacitor C2and resistor R17.

The ITH signal is provided to the main controller 1617 for driving mainswitches Q1 and Q2. The main controller 1617 is connected to a networkof resistors R2 and R3. The resistors are provided to sense the maininductor L1 current and provide the sensed main inductor L1 voltage. Thesensed main inductor L1 voltage is compared with the transient signalITH or a lower frequency component ITH_(DC) of the transient signal ITHvia a main comparator. The main comparator may be placed inside the maincontroller 1617. The main comparator is configured to receive at itsnon-inverting terminal the transient signal ITH or a lower frequencycomponent ITH_(DC) and at its inverting terminal the sensed maininductor L1 voltage. The main comparator compares the transient signalITH or a lower frequency component ITH_(DC) with the sensed maininductor L1 voltage.

If the transient signal ITH or a lower frequency component ITH_(DC) ismore than the sensed main inductor signal, the main comparator mayoutput a first main control signal. As described above, the first maincontrol signal may be a high signal configured to enable the mainswitching converter 1616 to source additional current to the outputterminal with the increased load current. If the transient signal ITH ora lower frequency component ITH_(DC) is less than the sensed maininductor signal, the main comparator may output a second main controlsignal. As described above, the second main control signal may be a lowsignal configured to enable the main switching converter 1616 to sinkadditional current from the output terminal with the decreased loadcurrent.

The transient signal ITH is also passed to the high pass filter 1624.The high pass filter 1636 includes a buffer 1636 a, a low pass filter1636 b, resistors R10-R13, an offset voltage V5, and an amplifier 1636c. The buffer 1636 a is configured to isolate the auxiliary controller1619 from the impedance of the feedback and compensation network 1622.The output of the buffer 1636 a is supplied to the non-invertingterminal of the amplifier 1636 c through the resistor R12. The output ofthe buffer 1636 a is also supplied to the inverting terminal of theamplifier 1636 c through the low pass filter 1636 b and the resistorR10. The low pass filter 1636 b includes a resistor R9 and a capacitorC10 and is configured to filter out the higher frequency componentITH_(AC) of the transient signal ITH and forward the lower frequencycomponent ITH_(DC) of the transient signal ITH to the inverting terminalof the amplifier 1636 c via the resistor R10.

The lower frequency component ITH_(DC) is subtracted from the transientsignal ITH (having both the higher frequency and lower frequencycomponents) and the difference is amplified by a K factor. As such, theoutput of the amplifier 1636 c may correspond to the amplified higherfrequency component ITH_(AC) of the transient signal ITH. The amplifiedhigher frequency component ITH_(AC) is supplied to ITH pin of theauxiliary controller 1616.

In one implementation, the resistors R10-R13 combined together provide again factor for the higher frequency component ITH_(AC) of the transientsignal ITH. The V_(offset) V5 may be provided so that during thesteady-state operation, the low frequency (or DC) current of theauxiliary switching converter 1618 is substantially zero. To this end,the V_(offset) V5 may be set to a value corresponding to half ripple ofthe high frequency (or AC) current such that during the steady-stateoperation average ripple AC current is substantially equal to zero.

The higher frequency component ITH_(AC) is provided to auxiliarycontroller 1619 for driving auxiliary switches Q3 and Q4. The auxiliarycontroller 1619 is connected to the resistor Rsense. The resistor Rsenseis provided to sense the auxiliary inductor L2 current and provide thesensed auxiliary inductor L2 voltage. The sensed auxiliary inductor L2voltage is compared with the high frequency component ITH_(AC) via anauxiliary comparator. The auxiliary comparator may be placed inside theauxiliary controller 1619. The auxiliary comparator is configured toreceive at its non-inverting terminal the amplified higher frequencycomponent ITH_(AC) and at its inverting terminal the sensed auxiliaryinductor L2 voltage. The auxiliary comparator compares the higherfrequency component ITH_(AC) with the sensed auxiliary inductor L2voltage.

If the higher frequency component ITH_(AC) is more than the sensedauxiliary inductor signal, the auxiliary comparator may output a firstauxiliary control signal. As described above, the first auxiliarycontrol signal may be a high signal configured to enable the auxiliaryswitching converter 1618 to source additional current to the outputterminal 1522 with the increased load current. If the higher frequencycomponent ITH_(AC) is less than the sensed auxiliary inductor signal,the auxiliary comparator may output a second auxiliary control signal.As described above, the second auxiliary control signal may be a lowsignal configured to enable the auxiliary switching converter 1618 tosink additional current from the output terminal with the decreased loadcurrent.

FIG. 16B illustrates a load transient performance comparison between afirst power supply system having single phase lower frequency buckconverter for handling both the lower frequency and higher frequencycomponents of the transient signal and a second power supply systemhaving a single phase lower frequency converter for handling lowerfrequency component of the transient signal and a higher frequencyconverter for handling high frequency component of the transient signal.The second power supply system may correspond to the system shown inFIG. 16A. As can be seen the peak-to-peak voltage ripple during the loadtransient condition in the first power supply system is 190 mV. Incontrast, the peak-to-peak voltage ripple during the transient conditionin the second power supply system is 88 mV. That is, the second powersupply system provides more than 50% transient ripple reduction, whilemaintaining similar efficiency in steady state operation.

FIG. 17 illustrates another exemplary circuit diagram of a feedbackcontrol mechanism 1700 configured to control a power supply systemhaving a main switching converter and an auxiliary switching converter.The feedback control mechanism 1700 may be used instead of the feedbackcontrol mechanism shown in FIGS. 6, 7, 10-12, and 15. The feedbackcontrol mechanism 1700 includes a feedback and compensation circuit1720, a main control circuit 1722, and an auxiliary control circuit1724. The feedback and compensation circuit 1720 is similar to thefeedback and compensation circuit 620 and therefore it is not describedfurther for brevity.

The auxiliary control circuit 1724 includes an auxiliary buffer 1724 a,which has a gain of K, a high pass filter 1724 b, an offset voltage 1724c, and an auxiliary comparator 1724 d. The auxiliary buffer 1724 a atone end is coupled to the feedback and compensation circuit 1720 and atanother end is coupled to the high pass filter 1724 b. The auxiliarybuffer 1724 a is configured to isolate the auxiliary control circuit1724 from an impedance of the feedback and compensation circuit 1720.The high pass filter 1724 b is coupled to the auxiliary buffer 1724 aand the offset voltage 1724 c. The high pass filter 1724 b is configuredto receive the transient signal ITH from the auxiliary buffer 1724 a andoutput a higher frequency component ITH_(AC) of the transient signalTIH. The high pass filter 1724 b includes a capacitor and a resistor.The capacitor at one end is connected to the auxiliary buffer 1724 a andat another end is connected to the offset voltage 1724 c. The resistorat one end is connected to the offset voltage 1724 c and at another endto the ground terminal.

The offset voltage 1724 c includes a positive terminal and a negativeterminal. The positive terminal of the offset voltage 1724 c is coupledto the non-inverting terminal of the auxiliary comparator 1724 d. Thenegative terminal of the offset voltage 1724 c is coupled to the highpass filter 1724 b. The auxiliary comparator 1724 d is configured toreceive the buffered higher frequency component of the transient signalplus the offset voltage at non-inverting terminal and a sensed highfrequency inductor voltage sourced by the auxiliary switching converterat the inverting terminal and generate an auxiliary control signal fordriving the auxiliary switching converter.

The offset voltage 1724 c is configured to offset high frequency currentsourced by the auxiliary switching converter to enable sourcingsubstantially zero average current from the auxiliary switchingconverter outside of the transient, during the steady state. Theauxiliary buffer 1724 a also amplifies the higher frequency component ofthe transient signal. This may be necessary since the feedback andcompensation circuit 1720 may attenuate the higher frequency componentof the transient signal as further described below.

The main control circuit 1722 includes a main comparator 1722 a and doesnot include a buffer and a low pass filter. The main comparator 1722 ais configured to receive the transient signal ITH directly from thefeedback and compensation circuit 1720 at its non-inverting terminal andsensed inductor current from the main switching converter and generate amain control signal. The main control signal is used to drive the mainswitching converter. To reduce the impact of the higher frequencycomponent ITH_(AC) of the transient signal ITH on the main switchingconverter, the higher frequency component ITH_(AC) of the transientsignal ITH may be attenuated by the compensation mechanism inside thefeedback and compensation circuit 1720. This may be accomplished basedon the values chosen for the resistors and capacitors in thecompensation circuit. Since the higher frequency component ITH_(AC) ofthe transient signal ITH is attenuated by the compensation circuit, themain control circuit 1722 may not need to filter out the high frequencycomponent ITH_(AC) and can utilize the transient signal ITH as-is todrive the main switching converter of the power supply system.

FIGS. 18A-18C illustrate exemplary load transient simulation waveformsfor the power supply system controlled by the feedback control mechanism1700 shown in FIG. 17. FIG. 18A illustrates the slower transient voltagesignal ITH 1812 and the higher frequency component ITH_(AC) 1814extracted and amplified from the slower transient voltage signal ITH1812. As shown, the higher frequency component ITH_(AC) 1814 has a sharprise in response to the positive edge of the current load step shown inFIG. 18C and then it slowly falls. Similarly, the higher frequencycomponent ITH_(AC) 1814 has a sharp fall in response to the negativeedge of the current load step shown in FIG. 18C and then it slowlyrises. In contrast, the slower transient voltage signal ITH 1812 has aslow rise in response to the positive edge of the current load stepshown in FIG. 18C and once it hits a given threshold level, it remainsat that given threshold level for the duration of the current load stepshown in FIG. 18C. Once the current load step terminates and in responseto the negative edge of the current load step shown in FIG. 18C, theslower transient voltage signal ITH 1812 slowly declines to a newthreshold level. As such, the slower transient voltage signal ITH 1812is not shown to fade away after the transient ends.

FIG. 18B illustrates low frequency regulator inductor current waveform1816 and high frequency regulator inductor current waveform 1818 duringtransients in the power supply system controlled by the feedback controlmechanism 1700 of FIG. 17. As shown, the low frequency regulatorinductor current waveform 1816 tracks the slower transient signal ITH1812, and the high frequency regulator inductor current waveform 1818tracks the higher frequency component ITH_(AC) 1814.

FIG. 18C illustrates output voltage overshoot 1820 a and undershoot 1820b for a load step 1822 during transients in the power supply systemcontrolled by the feedback control mechanism 1700 of FIG. 17. As shown,the voltage overshoot and undershoot for the power supply system isminimized in response to the transient.

FIG. 19 illustrates another exemplary circuit diagram of a feedbackcontrol mechanism 1900 configured to control a power supply systemhaving a main switching converter and an auxiliary switching converter.The feedback control mechanism 1900 is similar to the feedback controlmechanism 1200 except in the feedback control mechanism 1900 the controlcircuits 1922 and 1924 share a common RC filter 1928 in addition to acommon buffer 1926. Additionally, the auxiliary control circuit 1924includes an auxiliary buffer 1924 a, which is not shown in the auxiliarycontrol circuit 1224 of FIG. 12.

The common buffer 1926 is similar to the buffer 1226 of FIG. 12. Thecommon RC filter 1928 is a single RC filter shared among the controlcircuits 1922 and 1924. The common RC filter 1928 includes a resistor1928 a and a capacitor 1928 b. The common RC filter 1928 is configuredto provide the lower frequency component of the transient signal to themain control circuit 1922 and a higher frequency component of thetransient signal to the auxiliary control circuit 1924. The signalacross the capacitor 1928 b provides the lower frequency component ofthe transient signal and the differential signal across the resistor1928 a provides the higher frequency component of the transient signal.

The resistor 1928 a is coupled to an output terminal of the commonbuffer 1926 at one end and to a first node 1930 at another end. Thecapacitor 1928 b is coupled to the first node 1930 at one end and to aground terminal at another end. The main control circuit 1922 includes amain comparator having a non-inverting terminal and an invertingterminal. The non-inverting terminal is coupled to the first node 1930.The inverting terminal is coupled to a main inductor of the mainswitching converter. The main comparator is configured to receive thelower frequency component ITH_(DC) of the transient signal ITH fromacross the capacitor 1928 b at the non-inverting terminal and sensedmain inductor voltage at the inverting terminal and generate a maincontrol signal based on the lower frequency component ITH_(DC) of thetransient signal ITH for driving the main switching converter.

The auxiliary control circuit 1924 includes the auxiliary buffer 1924 aand an auxiliary comparator 1924 b having a non-inverting input terminaland an inverting input terminal. The auxiliary buffer 1924 a isconfigured to receive a higher frequency component ITH_(AC) of thetransient signal ITH from across the resistor 1928 a and provide thehigher frequency component ITH_(AC) of the transient signal ITH to thenon-inverting input terminal of the auxiliary comparator 1924 b throughan offset voltage 1924 c. The auxiliary comparator 1924 b is configuredto compare the higher frequency component ITH_(AC) of the transientsignal ITH received at the non-inverting input terminal and a sensedauxiliary inductor voltage sourced by the auxiliary switching converterand received at the inverting terminal and generate an auxiliary controlsignal for driving the auxiliary switching converter. The offset voltage1924 c is configured to offset high frequency current sourced by theauxiliary switching converter to enable sourcing substantially zeroaverage current from the auxiliary switching converter outside of thetransient, during the steady state. The auxiliary buffer 1924 a may havea gain factor and configured to amplify the higher frequency componentITH_(AC) of the transient signal ITH by its gain factor. This may benecessary since the feedback and compensation circuit 1920, similar tothe feedback and compensation circuit 1720, may attenuate the higherfrequency component ITH_(AC) of the transient signal ITH.

FIGS. 20A-20C illustrate exemplary load transient simulation waveformsfor the power supply system controlled by a feedback control mechanism1900 shown in FIG. 19. FIG. 20A illustrates the transient voltage signalITH 2010, the higher frequency component ITH_(AC) 2014 of the transientvoltage control signal ITH 2010, and the lower frequency componentITH_(DC) 2012 of the transient voltage control signal ITH 2010. Asshown, the transient voltage control signal ITH 2010 is a summation ofthe higher frequency component ITH_(AC) 2014 and the lower frequencycomponent ITH_(DC) 2012. The higher frequency component ITH_(AC) 2014has a sharp rise in response to the positive edge of the current loadstep shown in FIG. 20C then falls back. Similarly, the higher frequencycomponent ITH_(AC) 2014 has a sharp fall in response to the negativeedge of the current load step shown in FIG. 20C then rises back. Incontrast, the lower frequency component ITH_(DC) 2012 has a slow rise inresponse to the positive edge of the current load step shown in FIG. 20Cand once it hits a given threshold level, it remains at that giventhreshold level for the duration of the current load step shown in FIG.20C. Once the current load step terminates and in response to thenegative edge of the current load step shown in FIG. 20C, the lowerfrequency component ITH_(DC) 2012 slowly declines to a new thresholdlevel. As such, the lower frequency component ITH_(DC) 2012 is not shownto fade away after the transient ends.

FIG. 20B illustrates the low frequency regulator inductor currentwaveform 2016 and the high frequency regulator inductor current waveform2018 during transients in the power supply system controlled by thefeedback control mechanism 1900 shown in FIG. 19. As shown, the lowfrequency regulator inductor current waveform 2016 tracks the lowerfrequency component ITH_(DC) 2012, and the high frequency regulatorinductor current waveform 2018 tracks the higher frequency componentITH_(AC) 2014.

FIG. 20C illustrates output voltage overshoot 2020 a and undershoot 2020b for a load step 2022 in the power supply system controlled by thefeedback control mechanism 1900 shown in FIG. 19. As shown, the voltageovershoot and undershoot for the power supply system is minimized inresponse to the transient.

Instead of adding additional RC and buffer to the power interface, inone implementation, RC component of the compensation network may be usedto provide the low pass filter and high pass filter. In thisimplementation, the compensation network and the filtering network maybe combined into a single RC network to save component count. However,by using the compensation network to carry out the filtering networkfunctionality as well, one may comprise the responsiveness of thecircuit to the transient condition. This is mainly because there is nowless flexibility in choosing different value for compensation anddifferent value for filtering. As such, the power supply system of thisimplementation may have a longer settling time for higher frequencyconverter because the first priority is for the compensation circuit toensure the whole loop is stable rather than to change current from theslower channel to the faster channel. As such, the transition time fromthe faster supply to the slower supply here is longer. In contrast, inthe previous implementations there was a quicker transition from thefaster supply to the slower supply. Here, there is longer conductiontime for higher frequency converter. If the repetitive load transientdoes not happen frequently (e.g., once per minute) then the circuit cantolerate longer conduction time (e.g., burning more energy and consumemore power). However, if the repetitive load transient happensfrequently, then the higher frequency converter would be exposed totemperature rise, which reduces efficiency.

FIG. 21A illustrates another exemplary circuit diagram of a feedbackcontrol mechanism 2100A configured to control a power supply systemhaving a main switching converter and an auxiliary switching converter.The feedback control mechanism 2100A have a combined compensationnetwork and a filtering network. The feedback control mechanism 2100A issimilar to the feedback control mechanism 1900 except that in thefeedback control mechanism 2100A, the feedback and compensationmechanism 2120 carries out the filtering functionality instead of anadditional RC located outside of the feedback and compensationmechanism. To this end, the control circuits 2122 and 2124 do notinclude an RC filter or a buffer. In this implementation, the signalacross the capacitor C_(TH) in the compensation network 2120 providesthe lower frequency component of the transient signal and thedifferential signal across the resistor R_(TH) in the compensationnetwork 2120 provides the higher frequency component ITH_(AC) of thetransient signal ITH.

FIGS. 21B-21D illustrate exemplary load transient simulation waveformsfor the power supply system controlled by the feedback control mechanism2100A shown in FIG. 21A. FIG. 21B illustrates the transient voltagecontrol signal ITH 2130 and the higher frequency component ITH_(AC) 2132of the transient voltage control signal ITH 2130. As shown, the higherfrequency component ITH_(AC) 2132 has a sharp rise in response to thepositive edge of the current load step shown in FIG. 21D and falls back.Similarly, the higher frequency component ITH_(AC) 2132 has a sharp fallin response to the negative edge of the current load step shown in FIG.21D and rises back.

FIG. 21C illustrates low frequency main inductor current waveform 2134and high frequency auxiliary inductor current waveform 2136 duringtransients in the power supply system controlled by the feedback controlmechanism 2100A shown in FIG. 21A. The low frequency main inductorcurrent waveform 2134 tracks the transient voltage control signal ITH2130, and the high frequency auxiliary inductor current waveform 2136tracks the higher frequency component ITH_(AC) 2132.

FIG. 21D illustrates output voltage overshoot 2138 b and undershoot 2138a for a load step 2140 in the power supply system controlled by thefeedback control mechanism 2100A shown in FIG. 21A. As shown, thevoltage overshoot and undershoot for the power supply system isminimized in response to the transient compared to the conventionalpower supply system not utilizing an auxiliary switching converter asshown for example in FIG. 16B.

All of the power supply systems discussed so far share a common powersource for both the main switching converter and the auxiliary switchingconverter. To further increase the switching frequency or be moreflexible, in one implementation, the power source may be separated forthe main switching converter and the auxiliary switching converter.Since the auxiliary switching converter has a higher switchingfrequency, it has a higher switching loss; therefore, by reducing itsinput power source voltage, its frequency can be further increasedwithout increased power loss.

FIG. 22 illustrates another exemplary power supply system 2200 includingtwo separate control signals for driving a main switching converter andan auxiliary switching converter. In the power supply system 2200 aninput voltage of the main switching converter is different from theinput voltage of the auxiliary switching converter. The power supplysystem 2200 includes a power source 2210, a load device 2212, and apower interface 2214 coupled to the power source 2210 and the loaddevice 2212.

The power source 2210 may be any power source such as, a battery, agrid, a solar photovoltaic cells, AC generator, and an output voltagerail of a front-end supply. In this specific example, the power sourceis a DC power source implemented to generate 12 volts. The transientload 2212 may be any load such as, for example, a resistive load, aheater, a capacitive load, an inductive load, etc. The power interface2214 includes a main switching converter 2216, an auxiliary switchingconverter 2218, and a bias supply 2220, a feedback control mechanism(not shown). The feedback control mechanism may be any of the feedbackcontrol mechanisms previously discussed and may include a feedback andcompensation circuit, a main control circuit, and an auxiliary controlcircuit.

The input of the main switching converter 2216 is coupled to the powersource 2210, and the output of the main switching converter 2216 iscoupled to the load device 2212. The main switching converter 2216 isalso connected in parallel with the auxiliary switching converter 2218.The output of the auxiliary switching converter 2218 is coupled to theoutput of the main switching converter 2216. The input of the auxiliaryswitching converter 2218 is coupled to the bias supply 2220, which inturn is connected to the input of the main switching converter 2216.

The main switching converter 2216 may be of different topologies (e.g.,a buck, a boost, a resonant, etc.) and may be configured to conduct onlya low frequency current. To this end, the main switching converter 2216may be switching at a lower frequency for good efficiency. On the otherhand, the auxiliary switching converter 2218 may be configured toconduct only a high frequency AC current. To this end, the auxiliaryswitching converter 2218 may be switching at a higher frequency to trackhigh frequency transient ITH_(AC). In this manner, the auxiliaryswitching converter 2218 may have a high or higher power loss than themain switching converter 2216; however, this power loss may be limitedin time. This limited time may correspond to the duration of thetransient condition at the load device 2212. The average DC current ofthe auxiliary switching converter 2218 is near zero in steady state.

To further increase the switching frequency, the auxiliary switchingconverter 2218 is powered by the bias supply 2220. The bias supply 2220may only maintain DC bias on C_(IN) _(_) _(AC), average DC current beingapproximately 0 A. The bias supply 2220 can be a low power linearregulator supply or a low power switching mode power supply. In thisexample, the bias supply 2220 is configured to further reduce theauxiliary supply input voltage from 12 volt to 3.3 volts to reduce powerloss and increase efficiency of the power supply system 2200. C_(IN)_(_) _(AC) stores the energy (C·V²/2) for load transient from the outputof the auxiliary switching converter 2218. Since the C_(IN) _(_) _(AC)voltage is much higher than the output voltage, the required capacitanceof C_(IN) _(_) _(AC) is much smaller than the C_(OUT) capacitance.

FIG. 23 illustrates an exemplary power supply system 2300 similar to thepower supply system 2200 expect that the auxiliary switching converterhas a separate power source. As such, the power supply system 2300 mayhave the same performance in response to the transient conditions asthat of the power supply system 2200, except that the power supplysystem 2200 does not require a separated bias supply for the auxiliarysupply input if a separate power source is already available in asystem.

FIG. 24 illustrates an exemplary circuit diagram 2400 for the powersupply system 2300 shown in FIG. 23. The circuit diagram 2400 includespower sources 2410 and 2411, main switching converter 2416, an auxiliaryswitching converter 2418, a load device 2412, and a control mechanism2419.

The power sources 2410 and 2411 are configured to output a certainstandard voltage. To this end, the power sources 2410 and 2411 may be anelectrical outlet. Most single phase alternating-current electricaloutlets in the world supply power at 210-240 V or at 100-120 V.Alternatively, the power source 2410 and 2411 may include other types ofpower sources such as, for example, a battery, a solar photovoltaic, anAC generator, or a DC output voltage of a front-end power supply. Thepower source 2411 may supply power at a lower voltage than the powersource 2410. The power source 2411 may only supply high frequencytransient current.

Regardless of the type, usually the power sources 2410 and 2411 providea voltage different than the required voltage for the load device 2412.The provided voltage may be higher or lower than the required voltagefor the load device 2412. To match the source voltage to the loadvoltage, the power supply system 2400 includes the main switchingconverter 2416 and the auxiliary switching converter 2418.

The main switching converter 2416 and the auxiliary switching converter2418 are configured to change their respective input voltages to anappropriate voltage for the load device 2412. As noted above, theappropriate voltage for the load device 2412 may be higher or lower thanthe voltages 2410 and 2411. In one implementation, the appropriatevoltage for the load device 2412 is lower than the voltage of theelectrical power sources 2410 and 2411. The load device 2412 may includea resistive load, a magnetic load, a capacitive load, a heater, ormodern electronic devices.

The input of the main switching converter 2416 is coupled to the powersource 2410 and the output of the main switching converter 2416 iscoupled to the load device 2412. The main switching converter 2416includes a first main switch 2416 a, a second main switch 2416 b, a maininductor 2416 c, and a main inverter 2416 d. The first main switch 2416a and the second main switch 2416 b include MOSFETs. In one specificexample, as shown, the MOSFETs are N-Channel MOSFETs. The drain terminalof the first main switch 2416 a is coupled to the power source 2410 andthe source terminal of the first main switch 2416 a is coupled to a mainnode 2416 e. The gate terminal of the first main switch 2416 a iscoupled to a main control signal PWM_(DC). The gate terminal of thesecond main switch 2416 b is coupled to the main inverter 2416 d, whichis configured to supply the inverse of the main control signal PWM_(DC)to the gate of the second main switch 2416 b. The source terminal of thesecond main switch 2416 b is coupled to the ground. The drain terminalof the second main switch 2416 b is coupled to the main node 2416 e. Theinductor 2416 c at one end is coupled to the main node 2416 e and atanother end is coupled to the load device 2412.

The main switching converter 2416 may operate at a lower switchingfrequency than that of the auxiliary switching converter 2418.Therefore, the main switching converter 2416 may have a slower responsetime to the transients at the load device 2412. The auxiliary switchingconverter 2418 may operate at a higher switching frequency than that ofthe main switching converter 2418. Therefore, the auxiliary switchingconverter 2418 may have a faster response time to the transients at theload device 2412. Due to the higher switching frequency, the auxiliaryswitching converter 2418 may also have a more power loss than that ofthe main switching converter 2416. As noted above, the auxiliaryswitching converter 2418 may run from a lower power source 2411. Thismay allow the auxiliary switching converter 2418 to have very highswitching frequency, lower switching losses, lower voltage FET, largerduty-cycle, and relaxed Ton_min.

The auxiliary switching converter 2418 includes a first auxiliary switch2418 a, a second auxiliary switch 2418 b, an auxiliary inductor 2418 c,and an auxiliary inverter 2418 d. The first auxiliary switch 2418 a andthe second auxiliary switch 2418 b include MOSFETs. In one specificexample, as shown, the MOSFETs are N-Channel MOSFETs. The drain terminalof the first auxiliary switch 2418 a is coupled to the power source 2411and the source terminal of the first auxiliary switch 2418 a is coupledto an auxiliary node 2418 e. The gate terminal of the first auxiliaryswitch 2418 a is coupled to an auxiliary control signal PWM_(AC). Thegate terminal of the second auxiliary switch 2418 b is coupled to theauxiliary inverter 2418 d, which is configured to supply the inverse ofthe auxiliary control signal PWM_(AC) to the gate of the secondauxiliary switch 2418 b. The source terminal of the second auxiliaryswitch 2418 b is coupled to the ground. The drain terminal of the secondauxiliary switch 2418 b is coupled to the auxiliary node 2418 e. Theinductor 2418 c at one end is coupled to the auxiliary node 2418 e andat another end is coupled to the load device 2412.

The control mechanism 2419 includes a feedback and compensation circuit2420, a main control circuit 2422, and an auxiliary control circuit2424. The configuration of the control mechanism 2419 is similar tothose of the circuit diagram 1700 shown in FIG. 17. Specifically, thefeedback and compensation circuit 2420 is similar to the feedback andcompensation circuit 1720; the main control circuit 2422 is similar tothe main control circuit 1722 and the auxiliary control circuit 2424 issimilar to the auxiliary control circuit 1724. The main control circuit2422 includes a main comparator. The main comparator is configured toreceive the transient signal ITH directly from the feedback andcompensation circuit 2420 at its non-inverting terminal and sensed maininductor current from the main switching converter 2416 at its invertingterminal and generate the main control signal PWM_(DC).

The auxiliary control circuit 2424 includes an auxiliary gain buffer2424 a, a single high pass filter 2424 b, an offset voltage 2424 c, andan auxiliary comparator 2424 d. The auxiliary buffer 2424 a at one endis coupled to the feedback and compensation circuit 2420 and at anotherend is coupled to the high pass filter 2424 b. The auxiliary buffer 2424a is configured to isolate the auxiliary control circuit 2424 from animpedance of the feedback and compensation circuit 2420. The high passfilter 2424 b is coupled to the auxiliary buffer 2424 a and the offsetvoltage 2424 c. The high pass filter 2424 b is configured to receive thetransient signal from the buffer 2424 a and output a higher frequencycomponent of the transient signal. The high pass filter 2424 b includesa capacitor and a resistor. The capacitor at one end is connected to theauxiliary buffer 2424 a and at another end is connected to the offsetvoltage 2424 c. The resistor at one end is connected to the offsetvoltage 2424 c and at another end to the ground terminal.

The offset voltage 2424 c includes a positive terminal and a negativeterminal. The positive terminal of the offset voltage 2424 c is coupledto the non-inverting terminal of comparator 2424 d. The negativeterminal of the offset voltage 2424 c is coupled to the high pass filter2424 b. The auxiliary comparator 2424 d is configured to receive thebuffered higher frequency component of the transient signal offset bythe offset voltage at its non-inverting terminal and a sensed highfrequency inductor voltage sourced by the auxiliary switching converter2418 at its inverting terminal and generate an auxiliary control signalPWM_(AC) for driving the auxiliary switching converter 2418.

The offset voltage 2424 c is configured to offset high frequency currentsourced by the auxiliary switching converter 2418 to enable sourcingsubstantially zero average current from the auxiliary switchingconverter 2418 outside of the transient, during the steady state. Theauxiliary buffer 2424 a also amplifies the higher frequency componentITH_(AC) of the transient signal ITH. This may be necessary since thefeedback and compensation circuit 2420 may attenuate the higherfrequency component ITH_(AC) of the transient signal ITH.

FIGS. 25A-25C illustrate exemplary load transient simulation waveformsfor the power supply system 2400 shown in FIG. 24. In the power supplysystem 2400, the power source 2411 may only provide high frequencytransient current. The high frequency current therefore may have largeripple caused by load transient. The average input current on the powersource 2411 may be zero.

FIG. 25A illustrates the transient voltage signal V[ITH] 2512 and ahigher frequency component V[ITH_(AC)] 2510. As shown, the higherfrequency component V[ITH_(AC)] 2510 has a sharp rise in response to thepositive edge of the current load step shown in FIG. 25C and then itslowly falls. Similarly, the higher frequency component V[ITH_(AC)] 2510has a sharp fall in response to the negative edge of the current loadstep shown in FIG. 25C and then it slowly rises. In contrast, thetransient voltage signal V[ITH] 2512 has a slow rise in response to thepositive edge of the current load step shown in FIG. 25C and once ithits the given threshold, it stays at the given threshold until thecurrent load step terminates. In response to the negative edge of thecurrent load step shown in FIG. 25C, the transient voltage signal V[ITH]2512 slowly falls until it reaches the new threshold.

FIG. 25B illustrates low frequency main inductor current waveform 2514and high frequency auxiliary inductor current waveform 2516 duringtransients in the power supply system 2400 shown in FIG. 24 The lowfrequency main inductor current waveform 2514 tracks the transientvoltage signal V[ITH] 2512, and the high frequency auxiliary inductorcurrent waveform 2516 tracks the higher frequency component V[ITH_(AC)]2510.

FIG. 25C illustrates output voltage overshoot 2518 a and undershoot 2518b for a load step 2520 in the power supply system 2400 shown in FIG. 24.As shown, the peak-to-peak voltage ripple during the transient conditionin the power supply system 2400 is about 33 my which is substantiallybelow the peak-to-peak voltage ripple during the transient condition inthe power supply system including only a main switching converter.

In one implementation, since the auxiliary switching converter providesonly a high frequency (or AC) current during load transients and its lowfrequency (or DC) current is near 0 A outside of the transient, theauxiliary switching converter may not require an input power source.Instead, the auxiliary switching converter may only use a capacitor asits input power source. In this implementation, during a stable outputcondition, the power supply system may borrow some energy from the mainswitching converter output to charge up the capacitive power source ofthe auxiliary switching converter. During load transients, the powersupply system may use the charged capacitor to help increase transientresponse. For example, during the load step up, current is supplied fromthe capacitor to the output to quickly supply the extra current neededby the load. In contrast, during the load step down, the current issupplied to the capacitor from the output to charge the capacitor.

FIG. 26 illustrates another exemplary power supply system 2600 includingtwo separate control signals for driving a main switching converter andan auxiliary switching converter. The power supply system 2600 issimilar to the power supply system 2300 expect that the auxiliaryswitching converter is powered by a capacitor C_(IN) _(_) _(AC) insteadof a DC power source. The capacitor C_(IN) _(_) _(AC) is configured tostore the energy for V_(out) transient. The capacitor C_(IN-AC) can uselow cost, high capacitance and high ESR capacitors. The capacitorC_(IN-AC) can be charged up from output terminal. Therefore, thecapacitor C_(IN-AC) does not require input power source.

The power supply system 2600 includes a main power source 2610, a loaddevice 2612, a main switching converter 2616, and an auxiliary switchingconverter 2618. The main power source 2610, the load device 2612, themain switching converter 2616 are similar to the main power source 2310,the load device 2312, and the main switching converter 2216,respectively. Therefore, they are not described in more details forbrevity.

The auxiliary switching converter 2618 may be a bidirectional auxiliaryswitching converter configured to source high frequency current to theoutput terminal from the capacitor C_(IN-AC) during the load step up ofthe load transient conditions. Similarly, the auxiliary switchingconverter 2618 may be configured to sink current from the outputterminal during the load step down transient conditions or from the mainswitching converter 2616 during the steady state condition to thecapacitor C_(IN-AC) to charge the capacitor C_(IN-AC). To this end, theauxiliary switching converter 2618 is configured to support fast V_(out)transient and slow V_(IN-AC) bias regulation. In one specificimplementation, when the power supply system 2600 starts, it borrowssome energy from its output to charge up the capacitor C_(IN-AC) anduses the charged capacitor C_(IN-AC) during the transient to helpspeed-up the transient response.

FIG. 27 illustrates an exemplary circuit diagram 2700 for the powersupply system 2600 shown in FIG. 26. The circuit diagram 2700 includesthree compensation loops. The three compensation loops include a mainsupply V_(OUT) control compensation loop 2720, an auxiliary supplyV_(OUT) control compensation loop, and a lower frequency auxiliarysupply input V_(INAC) regulation compensation loop. The main supplyV_(OUT) control compensation loop is configured to provide a maincontrol signal PWM_(DC) to the main switching converter to respond tothe output transient condition. The main control signal PWM_(DC) may bebased on a lower frequency component ITH_(DC) of the transient signalITH. Alternatively, the main control signal PWM_(DC) may be based on thetransient signal ITH including both the lower frequency componentITH_(DC) and the higher frequency component ITH_(AC); however, thehigher frequency component ITH_(AC) may be attenuated with the loopcompensation design.

The auxiliary supply V_(OUT) control compensation loop is configured toprovide an auxiliary control signal PWM_(AC) to the auxiliary switchingconverter to respond to the output transient condition. The auxiliarycontrol signal PWM_(AC) may be based on a higher frequency componentITH_(AC) of the compensation signal ITH. The low frequency auxiliarysupply input V_(INAC) compensation loop is configured to regulate theinput capacitor voltage V_(IN) _(_) _(AC) of the auxiliary supply with aslow compensation and regulation.

The power supply system 2700 includes power sources 2710 and 2711, mainswitching converter 2716, an auxiliary switching converter 2718, a loaddevice 2712, and a control mechanism 2719. The power sources 2710 and2711 are configured to output a certain standard voltage. The powersources 2710 may be an electrical outlet. Most single phasealternating-current electrical outlets in the world supply power at210-240 V or at 100-120 V. Alternatively, the power source 2710 mayinclude other types of power sources such as, for example, a battery, asolar photovoltaic, an AC generator, or a DC output voltage of afront-end power supply. The power source 2711 may be a capacitor. Thepower source 2711 may supply power at a lower voltage than the powersource 2710. The power source 2711 may only supply high frequencytransient current.

Regardless of the type, usually the power sources 2710 and 2711 providea voltage different than the required voltage for the load device 2712.The provided voltage may be higher or lower than the required voltagefor the load device 2712. To match the source voltage to the loadvoltage, the power supply system 2700 includes the main switchingconverter 2716 and the auxiliary switching converter 2718.

The main switching converter 2716 and the auxiliary switching converter2718 are configured to change their respective input voltages to anappropriate voltage for the load device 2712. As noted above, theappropriate voltage for the load device 2712 may be higher or lower thanthe voltages 2710 and 2711. In one implementation, the appropriatevoltage for the load device 2712 is lower than the voltage of theelectrical power sources 2710 and 2711. The load device 2712 may includea resistive load, a magnetic load, a capacitive load, a heater, ormodern electronic devices.

The input of the main switching converter 2716 is coupled to the powersource 2710 and the output of the main switching converter 2716 iscoupled to the load device 2712. The main switching converter 2716includes a first main switch 2716 a, a second main switch 2716 b, a maininductor 2716 c, and a main inverter 2716 d. The first main switch 2716a and the second main switch 2716 b include MOSFETs. In one specificexample, as shown, the MOSFETs are N-Channel MOSFETs. The drain terminalof the first main switch 2716 a is coupled to the power source 2710 andthe source terminal of the first main switch 2716 a is coupled to a mainnode 2716 e. The gate terminal of the first main switch 2716 a isconfigured to receive a main control signal PWM_(DC) from the controlmechanism 2719. The gate terminal of the second main switch 2716 b iscoupled to the main inverter 2716 d, which is configured to supply theinverse of the main control signal PWM_(DC) to the gate of the secondmain switch 2716 b. The source terminal of the second main switch 2716 bis coupled to the ground. The drain terminal of the second main switch2716 b is coupled to the main node 2716 e. The inductor 2716 c at oneend is coupled to the main node 2716 e and at another end is coupled tothe load device 2712.

The main switching converter 2716 may operate at a lower switchingfrequency than that of the auxiliary switching converter 2718.Therefore, the main switching converter 2716 may have a slower responsetime to the transients at the load device 2712, and the auxiliaryswitching converter 2718 may have a faster response time to thetransients at the load device 2712. Due to the higher switchingfrequency, the auxiliary switching converter 2718 may also have a morepower loss than that of the main switching converter 2716. As notedabove, the auxiliary switching converter 2718 may run from a lower powersource 2711. This may allow the auxiliary switching converter 2718 tohave very high switching frequency, lower switching losses, lowervoltage FET, larger duty-cycle, and relaxed Ton_min.

The auxiliary switching converter 2718 includes a first auxiliary switch2718 a, a second auxiliary switch 2718 b, an auxiliary inductor 2718 c,and an auxiliary inverter 2718 d. The first auxiliary switch 2718 a andthe second auxiliary switch 2718 b include MOSFETs. In one specificexample, as shown, the MOSFETs are N-Channel MOSFETs. The drain terminalof the first auxiliary switch 2718 a is coupled to the input capacitorC_(IN) _(_) _(AC) 2711 and the source terminal of the first auxiliaryswitch 2718 a is coupled to an auxiliary node 2718 e. The gate terminalof the first auxiliary switch 2718 a is configured to receive anauxiliary control signal PWM_(AC) from the control mechanism 2719. Thegate terminal of the second auxiliary switch 2718 b is coupled to theauxiliary inverter 2718 d, which is configured to supply the inverse ofthe auxiliary control signal PWM_(AC) to the gate of the secondauxiliary switch 2718 b. The source terminal of the second auxiliaryswitch 2718 b is coupled to the ground. The drain terminal of the secondauxiliary switch 2718 b is coupled to the auxiliary node 2718 e. Theinductor 2718 c at one end is coupled to the auxiliary node 2718 e andat another end is coupled to the load device 2712.

The control mechanism 2719 includes a feedback and compensation circuit2720, a main control circuit 2722, an auxiliary control circuit 2724, anauxiliary input V_(INAC) feedback and regulation circuit 2730. Thefeedback and compensation circuit 2720 and the main control circuit 2722are similar to the feedback and compensation circuit 2420 and the maincontrol circuit 2422 shown and described with respect to FIG. 24,respectively. Therefore, they are not described further for brevity ofthe description.

The auxiliary control circuit 2724 includes a first gain buffer 2724 a,a single high pass filter 2724 b, a second gain buffer 2724 c, and acomparator 2724 d. The first gain buffer 2724 a at one end is coupled tothe feedback and compensation circuit 2720 and at another end is coupledto the high pass filter 2724 b. The first gain buffer 2724 a isconfigured to isolate the auxiliary control circuit 2724 from animpedance of the feedback and compensation circuit 2720. The high passfilter 2724 b is coupled to the first gain buffer 2724 a, the secondgain buffer 2724 c, and the comparator 2724 d. The high pass filter 2724b is configured to receive the transient signal ITH from the first gainbuffer 2724 a and output a higher frequency component ITH_(AC) of thetransient signal ITH. The high pass filter 2724 b includes a capacitorand a resistor. The capacitor at one end is connected to the first gainbuffer 2724 a and at another end is connected to the resistor and thenon-inverting terminal of the comparator 2724 d. The resistor at one endis connected to the non-inverting terminal of the comparator 2724 d andat another end to the second gain buffer 2724 c.

The second gain buffer 2724 c has an input terminal and an outputterminal and has an inverting gain factor K2. The output terminal of thesecond gain buffer 2724 c is coupled to one end of the resistor of thehigh pass filter 2724 b. The other end of the resistor of the high passfilter is coupled to the non-inverting terminal of the comparator 2724d. The input terminal of the second gain buffer 2724 c is coupled to theoutput of the feedback and regulation circuit 2730.

The comparator 2724 d is configured to receive the buffered higherfrequency component ITH_(AC) of the transient signal ITH at itsnon-inverting terminal and a sensed high frequency inductor voltagesourced by the auxiliary switching converter 2718 at its invertingterminal and generate an auxiliary control signal PWM_(AC) for drivingthe auxiliary switching converter 2718.

The auxiliary input V_(INAC) feedback and regulation circuit 2730 isconnected at one end to the power source 2711 and at the other end tothe auxiliary control circuit 2724 for driving the auxiliary switchingconverter 2718. The auxiliary input V_(INAC) feedback and regulationcircuit 2730 includes a feedback voltage sense circuit 2732, an erroramplifier 2734, and a compensation circuit 2736.

The feedback voltage sense circuit 2732 is configured to sense theV_(INAC) voltage of the capacitor 2711 through a network of resistors R1and R2. The network of resistors R1 and R2 form a resistor divider andscale the voltage of the capacitor 2711 to make it proportional toV_(ref2). The resistor R1 is coupled to the capacitor 2711 at one endand at another end is coupled to an inverting terminal of the erroramplifier 2734 and to the resistor R2. The resistor R2 at one end iscoupled to the inverting terminal of the error amplifier 2734 and to theresistor R1 and at another end is coupled to the ground terminal.

The feedback voltage sense circuit 2732 outputs a feedback voltageV_(fb) to the inverting terminal of the error amplifier 2734. The erroramplifier 2734 may be either a current-output type transconductanceamplifier or voltage-output type amplifier. The error amplifier 2734monitors the feedback voltage V_(fb) that is proportional to the voltageof capacitor 2711 at its inverting terminal and a reference voltageV_(ref2) at its non-inverting input. The feedback voltage V_(fb) at theinverting terminal of the error amplifier 2734 should be approximatelyequal to the reference voltage V_(ref2) at the non-inverting terminal ofthe error amplifier 2734. When these two voltages are not equal, theerror amplifier 2734 may provide a control signal at its output. Theoutput voltage of the error amplifier 2734 may correspond to thedifference between the actual input voltage and the desired inputvoltage of the capacitor 2711.

The compensation circuit 2736 includes capacitors C1 and C2 and aresistor R3 to provide frequency compensation for the feedback loop. Thecapacitor C1 is connected at one end to an output of the amplifier 2734and at another end to the ground terminal. The resistor R3 is connectedat one end to the output of the error amplifier 2734 and at another endto the capacitor C2. The capacitor C2 at one end is connected to theresistor R3 and at another end to the ground terminal.

The output of the feedback and regulation circuit 2730 is provided tothe auxiliary control circuit 2724. The auxiliary control circuit 2724is configured to control the auxiliary switching converter 2718 tocharge the capacitor 2711 based on the output of the feedback andregulation circuit 2730. In steady state mode, if the V_(INAC) voltageon capacitor 2711 is lower than the regulated level, the error amplifier2734 increases its output voltage, therefore decreases the voltage onthe non-inverting terminal of the comparator 2724 d through the secondgain buffer 2724 c. As a result, the auxiliary inductor 2718 c providesnegative current to charge capacitor 2711 from V_(OUT) and raises theV_(INAC) voltage back to the regulated level. On the other hand, if theV_(INAC) voltage on capacitor 2711 is higher than the regulated level,the error amplifier 2734 decreases its output voltage, thereforeincreases the voltage on the non-inverting terminal of the comparator2724 d through the second gain buffer 2724 c. As a result, the auxiliaryinductor 2718 c provides current from capacitor 2711 to V_(OUT) todischarge the V_(INAC) voltage back to the regulated level.

FIGS. 28A-28D illustrate simulation waveforms for the circuit diagram2700 shown in FIG. 27. FIG. 28A illustrates the input capacitor voltageof the auxiliary switching converter 2718. As shown, during the loadstep up transient, the charged capacitor is discharged and as such theinput voltage V_(IN) _(_) _(AC) is first reduced then rises back to itsregulated level slowly. In contrast, during the load step downtransient, the capacitor is charged and as such the input voltage V_(IN)_(_) _(AC) is first increased then falls back to its regulated levelslowly.

FIG. 28B illustrates the higher frequency component V[ITH_AC] of thetransient voltage signal V[ITH] output by the high pass filter 2724 band the transient voltage signal V[ITH] output by the feedback andcompensation circuit 2720 in response to the detected transient. Thetransient voltage signal V[ITH] may include both the higher frequencycomponent V[ITH_AC] and the lower frequency component V[ITH_DC];however, the higher frequency component V[ITH_AC] may be attenuated byproper selection of components of the compensation circuit.

As shown, the higher frequency component V[ITH_AC] has a sharp rise inresponse to the positive edge of the current load step shown in FIG. 28Dand it slowly falls. Similarly, the higher frequency component V[ITH_AC]has a sharp fall in response to the negative edge of the current loadstep shown in FIG. 28D and it slowly rises. In contrast, the transientvoltage signal V[ITH] has a slow rise in response to the positive edgeof the current load step shown in FIG. 28D and once it hits the giventhreshold, it stays at the given threshold until the current load stepterminates. In response to the negative edge of the current load stepshown in FIG. 28D, the transient signal V[ITH] slowly falls until itreaches the new threshold.

FIG. 28C similarly illustrates the auxiliary supply transient inductorcurrent I[Lac] increases as the input capacitor voltage decreases andthe auxiliary supply transient inductor I[Lac] current decreases as theinput capacitor voltage increases. Similarly, as shown, the main supplytransient inductor current I[Ldc] increases as the input capacitorvoltage decreases and the main supply transient inductor I[Ldc] currentdecreases as the input capacitor voltage increases. The main supplytransient inductor current I[Ldc] tracks the transient voltage signalV[ITH], and the auxiliary supply transient current I[Lac] tracks thehigher frequency component V[ITH_AC] of the transient signal V[ITH].

FIG. 28D illustrates output voltage overshoot 2818 a and undershoot 2818b for a load step I[Loadstep] in the power supply system 2700 shown inFIG. 27. As shown, the output voltage V[vout] dips during the load stepup since the current is supplied from the output capacitor to compensatefor additional current necessary by the load step up. The output voltageV[vout] increases during the load step down since the current issupplied to the output capacitor to compensate for reduced currentnecessary by the load step down.

FIG. 29 illustrates another exemplary circuit diagram 2900 for the powersupply system shown in FIG. 26 in which the power source for theauxiliary switching converter includes a capacitor. The circuit diagram2900 is similar to the circuit diagram 2700 in that the auxiliaryswitching converter is powered by an input capacitor. The circuitdiagram 2900 is different from the circuit diagram 2700 in that it hastwo separated compensations for the main switching converter and theauxiliary switching converter without any interconnections.Specifically, similar to the circuit diagram 1100 shown in FIG. 11, thecircuit diagram 2900 has an auxiliary control circuit with anindependent feedback and compensation circuit from the main controlcircuit.

The circuit diagram 2900 includes power sources 2910 and 2911, a mainswitching converter 2916, an auxiliary switching converter 2918, a loaddevice 2912, a main control loop 2919, an auxiliary control circuit2921, and an auxiliary input voltage source control loop 2930. The powersources 2910 and 2911 are configured to output a certain standardvoltage. The power source 2910 may be an electrical outlet. Most singlephase alternating-current electrical outlets in the world supply powerat 210-240 V or at 100-120 V. Alternatively, the power source 2910 mayinclude other types of power sources such as, for example, a battery, asolar photovoltaic, an AC generator, or a DC output voltage of afront-end power supply. The power source 2911 may be a capacitor. Thecapacitor may supply power at a lower voltage than the power source2910. The capacitor may only supply high frequency AC transient current.

Regardless of the type, usually the power sources 2910 and 2911 providea voltage different than the required voltage for the load device 2912.The provided voltage may be higher or lower than the required voltagefor the load device 2912. To match the source voltage to the loadvoltage, the power supply system 2900 includes the main switchingconverter 2916 and the auxiliary switching converter 2918.

The main switching converter 2916 and the auxiliary switching converter2918 are configured to change their respective input voltages to anappropriate voltage for the load device 2912. As noted above, theappropriate voltage for the load device 2912 may be higher or lower thanthe voltages 2910 and 2911. In one implementation, the appropriatevoltage for the load device 2912 is lower than the voltage of theelectrical power sources 2910 and 2911. The load device 2912 may includea resistive load, a magnetic load, a capacitive load, a heater, ormodern electronic devices.

The input of the main switching converter 2916 is coupled to the powersource 2910 and the output of the main switching converter 2916 iscoupled to the load device 2912. The main switching converter 2916includes a first main switch 2916 a, a second main switch 2916 b, a maininductor 2916 c, and a main inverter 29716 d. The first main switch 2916a and the second main switch 2916 b include MOSFETs. In one specificexample, as shown, the MOSFETs are N-Channel MOSFETs. The drain terminalof the first main switch 2916 a is coupled to the power source 2910 andthe source terminal of the first main switch 2916 a is coupled to a mainnode 2916 e. The gate terminal of the first main switch 2916 a iscoupled to the main control loop 2919 and is configured to receive amain control signal PWM_(DC). The gate terminal of the second mainswitch 2916 b is coupled to the main inverter 2916 d, which isconfigured to supply the inverse of the main control signal PWM_(DC) tothe gate of the second main switch 2916 b. The source terminal of thesecond main switch 2916 b is coupled to the ground. The drain terminalof the second main switch 2916 b is coupled to the main node 2916 e. Themain inductor 2916 c at one end is coupled to the main node 2916 e andat another end is coupled to the load device 2912.

The main switching converter 2916 may operate at a lower switchingfrequency than that of the auxiliary switching converter 2918.Therefore, the main switching converter 2916 may have a slower responsetime to the transients at the load device 2912 than that of theauxiliary switching converter 2918. Due to its higher switchingfrequency, the auxiliary switching converter 2918 may also have a morepower loss than that of the main switching converter 2916. As notedabove, the auxiliary switching converter 2918 may run from a lower powersource 2911. This may allow the auxiliary switching converter 2918 tohave very high switching frequency, lower switching losses, lowervoltage FET, larger duty-cycle, and relaxed Ton_min.

The auxiliary switching converter 2918 includes a first auxiliary switch2918 a, a second auxiliary switch 2918 b, an auxiliary inductor 2918 c,and an auxiliary inverter 2918 d. The first auxiliary switch 2918 a andthe second auxiliary switch 2918 b include MOSFETs. In one specificexample, as shown, the MOSFETs are N-Channel MOSFETs. The drain terminalof the first auxiliary switch 2918 a is coupled to the power source 2911and the source terminal of the first auxiliary switch 2918 a is coupledto an auxiliary node 2918 e. The gate terminal of the first auxiliaryswitch 2918 a is coupled to the auxiliary control loop 2921 and isconfigured to receive an auxiliary control signal PWM_(AC). The gateterminal of the second auxiliary switch 2918 b is coupled to theauxiliary inverter 2918 d, which is configured to supply the inverse ofthe auxiliary control signal PWM_(AC) to the gate of the secondauxiliary switch 2918 b. The source terminal of the second auxiliaryswitch 2918 b is coupled to the ground. The drain terminal of the secondauxiliary switch 2918 b is coupled to the auxiliary node 2918 e. Theauxiliary inductor 2918 c at one end is coupled to the auxiliary node2918 e and at another end is coupled to the load device 2912.

The main control loop 2919 is coupled at one end to the output terminaland at another end to the first main switch 2916 a and the main inverter2916 d. The main control loop 2919 includes a main feedback andcompensation circuit and a main control circuit (not shown). The mainfeedback and compensation circuit is similar to the feedback andcompensation circuit 2720 shown in FIG. 27. Similarly, the main controlcircuit is similar to the main control circuit 2722 shown in FIG. 27.Therefore, for the sake of brevity they are not further described. Themain control loop 2919 may be configured to provide a main controlsignal PWM_(DC) for controlling the main switching converter 2916 inresponse the transient condition.

The auxiliary control loop 2921 is coupled at one end to the outputterminal and at another end to the first auxiliary switch 2918 a and theauxiliary inverter 2918 d. The auxiliary control loop 2921 includes afeedback and compensation circuit 2920 and an auxiliary control circuit2924. The feedback and compensation circuit 2920 at one end is coupledto the output terminal and at another end is coupled to the auxiliarycontrol circuit 2924. As shown and unlike the feedback and compensationcircuit 2720, the feedback and compensation circuit 2920 is coupled toonly the auxiliary control circuit 2924 and not to the main controlcircuit. The feedback and compensation circuit 2920 includes a transientdetection circuit 2922, an amplifier 2923, and a compensation circuit2925. The transient detection circuit 2922 includes a resistor 2922 aand a capacitor 2922 b. The resistor 2922 a at one end is coupled to theoutput terminal and the inverting terminal of the amplifier 2923 and atanother end is coupled to the capacitor 2922 b. The capacitor 2922 b atone end is coupled to the resistor 2922 a and the non-inverting terminalof the amplifier 2923 and at another end is coupled to the groundterminal.

The resistor 2922 a and capacitor 2922 b forms a low pass filter andprovides the average V_(out) voltage as a reference voltage to the erroramplifier 2923 positive input terminal. The amplifier 2923 monitors theoutput voltage with respect to the averaged output voltage of thecapacitor 2922 b. When there is a transient event and these two voltagesare not equal, the amplifier 2923 may provide a control signal at itsoutput. The output voltage of the amplifier 2923 may correspond to thedifference between the actual output voltage and the desired averagedoutput.

The compensation circuit 2925 includes capacitors 2925 a and 2925 b anda resistor 2925 c to provide frequency compensation for the feedbackloop. The capacitor 2925 a is connected at one end to an output of theamplifier 2923 and at another end to the ground terminal. The resistor2925 c is connected at one end to the output of the amplifier 2923 andat another end to the capacitor 2925 b. The capacitor 2925 b at one endis connected to the resistor 2925 c and at another end to the groundterminal.

The output of the feedback and compensation circuit 2925 is provided tothe auxiliary control circuit 2924. The auxiliary control circuit 2924is configured to control the auxiliary switching converter 2918. Theauxiliary control circuit 2924 is similar to the auxiliary controlcircuit 2724. To this end, the auxiliary control circuit 2924 includes afirst gain buffer 2924 a, a high pass filter 2924 b, a second gainbuffer 2924 c, and an auxiliary comparator 2924 d.

The first gain buffer 2924 a at one end is coupled to the feedback andcompensation circuit 2920 and at another end is coupled to the high passfilter 2924 b. The first gain buffer 2924 a is configured to isolate theauxiliary control circuit 2924 from an impedance of the feedback andcompensation circuit 2920. The high pass filter 2924 b is coupled to thefirst gain buffer 2924 a, the second gain buffer 2924 c, and theauxiliary comparator 2924 d. The high pass filter 2924 b is configuredto receive the transient signal ITH from the first gain buffer 2924 aand output a higher frequency component ITH_(AC) of the transient signalITH. The high pass filter 2924 b includes a capacitor and a resistor.The capacitor at one end is connected to the first gain buffer 2924 aand at another end is connected to the resistor and the non-invertingterminal of the auxiliary comparator 2924 d. The resistor at one end isconnected to the non-inverting terminal of the comparator 2924 d and atanother end to the second gain buffer 2924 c.

The second gain buffer 2924 c has an input terminal and an outputterminal and has an inverting gain factor K2. The output terminal of thesecond gain buffer 2924 c is coupled to one end of the resistor of thehigh pass filter 2924 b. The other end of the resistor of the high passfilter is coupled to the non-inverting terminal of the auxiliarycomparator 2924 d. The input terminal of the second gain buffer 2924 cis coupled to the output of the auxiliary input voltage source controlloop 2930.

The auxiliary comparator 2924 d is configured to receive the bufferedhigher frequency component ITH_(AC) of the transient signal ITH at itsnon-inverting terminal and a sensed high frequency inductor voltagesourced by the auxiliary switching converter 2918 at its invertingterminal and generate an auxiliary control signal PWM_(AC) for drivingthe auxiliary switching converter 2918.

The auxiliary input voltage source control loop 2930 is connected at oneend to the power source 2911 and at the other end to the auxiliarycontrol circuit 2924 for driving the auxiliary switching converter 2918.The auxiliary input voltage source control loop 2930 includes a feedbackvoltage sense circuit 2932, an error amplifier 2934, and a compensationcircuit 2936. The feedback voltage sense circuit 2932 is configured tosense the voltage of the capacitor 2911 through a network of resistors2932 a and 2932 b. The network of resistors 2932 a and 2932 b form aresistor divider and scale the voltage of the capacitor 2911 to make itproportional to V_(ref). The resistor 2932 a is coupled to the capacitor2911 at one end and at another end is coupled to an inverting terminalof the error amplifier 2934 and to the resistor 2932 b. The resistor2932 b is coupled to the inverting terminal of the error amplifier 2934and to the resistor 2932 a at one end and at another end is coupled tothe ground terminal.

The feedback voltage sense circuit 2932 outputs a feedback voltageV_(fb) to the inverting terminal of the error amplifier 2934. The erroramplifier 2934 may be either a current-output type transconductanceamplifier or voltage-output type amplifier. The error amplifier 2934monitors the feedback voltage V_(fb) that is proportional to the voltageof capacitor 2911 at its inverting input and a reference voltage V_(ref)at its non-inverting input. The feedback voltage across resistor 2932 bshould be approximately equal to the reference voltage V_(ref) Whenthese two voltages are not substantially equal to each other, theamplifier 2934 may provide a control signal at its output. The outputvoltage of the amplifier 2934 may correspond to the difference betweenthe actual input voltage and the desired input voltage.

The compensation circuit 2936 includes capacitors 2936 a and 2936 b anda resistor 2936 c to provide frequency compensation for the feedbackloop. The capacitor 2936 a is connected at one end to an output of theamplifier 2934 and at another end to the ground terminal. The resistor2936 c is connected at one end to the output of the amplifier 2934 andat another end to the capacitor 2936 b. The capacitor 2936 b at one endis connected to the resistor 2936 c and at another end to the groundterminal.

The output of the auxiliary input voltage source control loop 2930 isprovided to the auxiliary control circuit 2924. The auxiliary controlcircuit 2924 is configured to control the auxiliary switching converter2918 to charge or discharge the capacitor 2911 based on the output ofthe auxiliary input voltage source control loop 2930. In steady statemode, if the V_(INAC) voltage on capacitor 2911 is lower than theregulated level, the error amplifier 2934 increases its output voltage,therefore decreases the voltage on the non-inverting terminal of theauxiliary comparator 2924 d through the second gain buffer 2924 c. As aresult, the auxiliary inductor 2918 c provides negative current tocharge capacitor 2911 from V_(OUT) and raises the V_(INAC) voltage backto the regulated level. On the other hand, if the V_(INAC) voltage oncapacitor 2911 is higher than the regulated level, the error amplifier2934 decreases its output voltage, therefore increases the voltage onthe non-inverting terminal of the auxiliary comparator 2924 d throughthe second gain buffer 2924 c. As a result, the auxiliary inductor 2918c provides current from capacitor 2911 to V_(OUT) to discharge theV_(INAC) voltage back to the regulated level.

FIGS. 30A-30E illustrate simulation waveforms for the circuit diagram2900 shown in FIG. 29. FIG. 30A illustrates the input capacitor voltageof the auxiliary switching converter. As shown, during the load step uptransient, the charged input capacitor is discharged and as such theinput voltage V_(in) _(_) _(AC) is reduced. The input voltage V_(in)_(_) _(AC) then slowly rises back to its regulated level. In contrast,during the load step down transient, the input capacitor is charged andas such the input voltage V_(in) _(_) _(AC) is increased. The inputvoltage V_(in) _(_) _(AC) then slowly falls back to its regulated level.

FIG. 30B illustrates the output voltage V_(OUT) in comparison with itsaveraged voltage V_(REF2) across capacitor 2922 b. As shown, during theload step up, the V_(OUT) falls below the filtered voltage of capacitor2922 b and during the load step down, the V_(OUT) exceeds the filteredvoltage of capacitor 2922 b.

FIG. 30C illustrates the higher frequency component V[ITH_AC] of thetransient voltage signal V[ITH] output by the high pass filter 2924 band the transient signal V[ITH] output by the feedback and compensationcircuit inside the main control loop 2919 in response to the detectedtransient. The transient signal V[ITH] may include both the higherfrequency component V[ITH_AC] and the lower frequency componentV[ITH_DC]; however, the higher frequency component V[ITH_AC] may beattenuated by proper selection of components of the compensationcircuit.

As shown, the higher frequency component V[ITH_AC] has a sharp rise inresponse to the positive edge of the current load step shown in FIG. 30Eand it slowly falls. Similarly, the higher frequency component V[ITH_AC]has a sharp fall in response to the negative edge of the current loadstep shown in FIG. 30E and it slowly rises. In contrast, the transientsignal V[ITH] has a slow rise in response to the positive edge of thecurrent load step shown in FIG. 30E and once it hits the giventhreshold, it stays at the given threshold until the current load stepterminates. In response to the negative edge of the current load stepshown in FIG. 30E, the transient signal V[ITH] slowly falls until itreaches the new threshold.

FIG. 30D illustrates the auxiliary switching converter transientinductor current I[Lac] increases as the input capacitor voltagedecreases and the auxiliary witching converter transient inductor I[Lac]current decreases as the input capacitor voltage increases. Similarly,as shown, the main switching converter transient inductor current I[Ldc]increases as the input capacitor voltage decreases and the mainswitching converter transient inductor I[Ldc] current decreases as theinput capacitor voltage increases. The main switching convertertransient inductor current I[Ldc] tracks the transient signal V[ITH],and the auxiliary switching converter transient current I[Lac] tracksthe higher frequency component V[ITH_AC] of the transient signal V[ITH].

FIG. 30E illustrates output voltage overshoot and undershoot for a loadstep I[Loadstep] in the power supply system 2900 shown in FIG. 29. Asshown, the output voltage V[vout] dips during the load step up since thecurrent is supplied from the output capacitor to compensate foradditional current necessary by the load step up. The output voltageV[vout] increases during the load step down since the current issupplied to the output capacitor to sunk current from the output.

FIG. 31 illustrates another exemplary power supply system 3100 with theauxiliary switching converter moved inside the same package of loaddevice for fast responding to load transient conditions. The powersupply system 3100 includes a power source 3110, a main switchingconverter 3114, and a load device package 3112. The load device package3112 includes an auxiliary switching converter 3116, a load device 3112a, and a voltage source 3112 b.

The main switching converter 3114 at one end is coupled to the powersource 3110 and at another end is coupled to the load device package3112. The main switching converter 3114 is configured to convert thevoltage of the power source 3110 to a voltage compatible with the loaddevice 3112 a.

The power source 3110 is configured to output a certain standardvoltage. The power source 3110 may be an electrical outlet. Most singlephase alternating-current electrical outlets in the world supply powerat 210-240 V or at 100-120 V. Alternatively, the power source 3110 mayinclude other types of power sources such as, for example, a battery, asolar photovoltaic, an AC generator, or a DC output voltage of afront-end power supply. Regardless of the type, usually the power source3110 provides a voltage different than the required voltage for the loaddevice 3112 a. The provided voltage may be higher or lower than therequired voltage for the load device 3112 a. To match the source voltageto the load voltage, the power supply system 3100 includes the mainswitching converter 3114 and an auxiliary switching converter 3116.

The main switching converter 3114 and the auxiliary switching converter3116 are configured to change their respective input voltages to anappropriate voltage for the load device 3112 a. The appropriate voltagefor the load device 3112 a may be higher or lower than the inputvoltages of the main switching converter 3114 and the auxiliaryswitching converter 3116. In one implementation, the appropriate voltagefor the load device 3112 a is lower than the voltage of the electricalpower sources for the main switching converter 3114 and the auxiliaryswitching converter 3116. The load device 3112 a may include a resistiveload, a magnetic load, a capacitive load, a heater, or modern electronicdevices.

Although not shown, the main switching converter 3114 includes mainswitches similar to the main switching converter 2916 shown in FIG. 29.Additionally, the main switching converter 3114 includes a main controlloop similar to the main control loop 2919 shown in FIG. 29.

The auxiliary switching converter 3116 is part of the load devicepackage 3112. The auxiliary switching converter 3116 at one end iscoupled to a transient load device 3112 a and at another end is coupledto a power source 3112 b. The power source 3112 b includes a capacitivepower source. The power source 3112 b may supply power at a lowervoltage than the power source 3110. The power source 3112 b may onlysupply high frequency transient current.

Although not shown, the auxiliary switching converter 3116 includes anauxiliary switches similar to the auxiliary switching converter 2918shown in FIG. 29. The auxiliary switching converter 3116 may alsoinclude an auxiliary control loop and an auxiliary input voltage sourcecontrol loop. The auxiliary control loop and the auxiliary input voltagesource control loop respectively are similar the auxiliary control loop2921 and the auxiliary input voltage source control loop 2930 shown inFIG. 29. Therefore, for the sake of brevity, they are not describedfurther.

FIG. 32A illustrates another exemplary power supply system 3200 in whichthe output of the auxiliary switching converter is connected to theinput of the main switching converter instead of to the load device toprovide the holdup time when the main power source is temporarydisconnected. The power supply system 3200 may be used for fast hold-uptime response circuit or input voltage transient absorber circuit. Forexample, in a computer system running from the AC line, if the AC linefails, 20 millisecond of power may be needed to keep the system alive tosave the work in progress when the main power source is not available.This energy may be stored on the input capacitor of the auxiliaryswitching converter and provided from the auxiliary supply.

As shown, the power supply system 3200 includes power sources 3210,3211, a main switching converter 3214, an auxiliary switching converter3216, and a load device 3212. The main switching converter 3214 at oneend is coupled to the power source 3210 and at another end is coupled tothe load device 3212. The main switching converter 3214 is configured toconvert the voltage of the power source 3210 to a voltage compatiblewith the load device 3212. The auxiliary switching converter 3216 at oneend is coupled to the power source 3211 and at another end is coupled tothe main switching converter 3214 and the power source 3210.

The power source 3210 is configured to output a certain standardvoltage. The power source 3210 may be an electrical outlet.Alternatively, the power source 3210 may include other types of powersources such as, for example, a battery, a solar photovoltaic, an ACgenerator, or a DC output voltage of a front-end power supply.Regardless of the type, usually the power source 3210 provides a voltagedifferent than the required voltage for the load device 3212. Theprovided voltage may be higher or lower than the required voltage forthe load device 3212. The power source 3211 may be an energy storagecapacitor. The power source 3211 may only supply high frequencytransient current to maintain the input voltage V_(IN) _(_) _(DC).

The main switching converter 3214 is configured to change its inputvoltages to an appropriate voltage for the load device 3212. The loaddevice 3212 may include a resistive load, a magnetic load, a capacitiveload, a heater, or modern electronic devices. The configurations of themain switching converter 3214 and the auxiliary switching converter 3216are described in more details with respect to FIG. 33.

FIGS. 32B-32E illustrate waveforms of the power supply system 3200 shownin FIG. 32A in response to the input voltage source of the main supplycome temporary disconnected. FIG. 32B illustrates the voltage of thecapacitor 3211 in response to the failure of the power source 3210. Asshown, the voltage of the capacitor 3211 reduces in response to thecurrent load step to source additional current to the input of the mainsupply 3214.

FIG. 32C illustrates the main supply inductor current I[Ldc] and theauxiliary supply inductor current I[Lac] supplied to the load device inresponse to the failure of the power source 3210. FIG. 32D illustratesthe voltage of the capacitor directly connected to the power source 3210and the capacitor 3211 voltage in response to the failure of the powersource 3210. FIG. 32E illustrates the output voltage of the power supplysystem. As shown, the output voltage does not change in response to thetemporary failure of the power source 3210.

FIG. 33 illustrates an exemplary circuit diagram 3300 for the powersupply system 3200 shown in FIG. 32. The circuit diagram 3300 includespower sources 3310 and 3311, a main switching converter 3316, anauxiliary switching converter 3318, a load device 3312, a main controlloop 3319, an auxiliary control loop 3321, and an auxiliary inputvoltage source control loop 3330. The power sources 3310 and 3311 weredescribed with respect to FIG. 32 and are not described further for thesake of brevity.

The main switching converter 3316 and the auxiliary switching converter3318 are configured to change their respective input voltages to anappropriate voltage for the load device 3312. The load device 3312 mayinclude a resistive load, a magnetic load, a capacitive load, a heater,or modern electronic devices.

The input of the main switching converter 3316 is coupled to the powersource 3310 through an inductor 3315 and the output of the mainswitching converter 3316 is coupled to the load device 3312. Theinductor 3315 can be an external input filter inductor, the parasiticinductor of the power source 3310 output, or the parasitic inductor ofthe power cable.

The main switching converter 3316 includes a first main switch 3316 a, asecond main switch 3316 b, a main inductor 3316 c, and a main inverter3316 d. The first main switch 3316 a and the second main switch 3316 binclude MOSFETs. In one specific example, as shown, the MOSFETs areN-Channel MOSFETs. The drain terminal of the first main switch 3316 a iscoupled to the power source 3310 through the inductor 3315 and thesource terminal of the first main switch 3316 a is coupled to a mainnode 3316 e. The gate terminal of the first main switch 3316 a iscoupled to the main control loop 3319 and is configured to receive amain control signal PWM_(DC). The gate terminal of the second mainswitch 3316 b is coupled to the main inverter 3316 d, which isconfigured to supply the inverse of the main control signal PWM_(DC) tothe gate of the second main switch 3316 b. The main control signalPWM_(DC) is generated from the main control loop 3319. The sourceterminal of the second main switch 3316 b is coupled to the ground. Thedrain terminal of the second main switch 3316 b is coupled to the mainnode 3316 e. The main inductor 3316 c at one end is coupled to the mainnode 3316 e and at another end is coupled to the load device 3312. Themain switching converter 3316 may operate at a lower switching frequencythan that of the auxiliary switching converter 3318.

The auxiliary switching converter 3318 at one end is coupled to the mainconverter input capacitor 3317 and the power source 3310 through aninductor 3315 and at another end is coupled to the power source 3311.The auxiliary switching converter 3318 includes a first auxiliary switch3318 a, a second auxiliary switch 3318 b, an auxiliary inductor 3318 c,and an auxiliary inverter 3318 d. The first auxiliary switch 3318 a andthe second auxiliary switch 3318 b include MOSFETs. In one specificexample, as shown, the MOSFETs are N-Channel MOSFETs. The drain terminalof the first auxiliary switch 3318 a is coupled to the power source 3311and the source terminal of the first auxiliary switch 3318 a is coupledto an auxiliary node 3318 e. The gate terminal of the first auxiliaryswitch 3318 a is coupled to an auxiliary control loop 3321 andconfigured to receive an auxiliary control signal PWM_(AC). The gateterminal of the second auxiliary switch 3318 b is coupled to theauxiliary inverter 3318 d, which is configured to supply the inverse ofthe auxiliary control signal PWM_(AC) to the gate of the secondauxiliary switch 3318 b. The auxiliary control signal PWM_(AC) isgenerated from the auxiliary control loop 3321. The source terminal ofthe second auxiliary switch 3318 b is coupled to the ground. The drainterminal of the second auxiliary switch 3318 b is coupled to theauxiliary node 3318 e. The auxiliary inductor 3318 c at a first end iscoupled to the auxiliary node 3318 e and at a second end is coupled tothe main converter input capacitor 3317 and the power source 3310through the inductor 3315. The second end of the auxiliary inductor 3318c is also connected to the drain of the first main switch 3316 a.

The main control loop 3319 includes a main feedback and compensationcircuit and a main comparator. The main feedback and compensationcircuit is similar to the feedback and compensation circuit 2720 shownin FIG. 27. Similarly, the main comparator is similar to the maincomparator 2722 shown in FIG. 27. Therefore, for the sake of brevity,the main feedback and compensation circuit and the main comparatorcircuit are not described in more details. The main control loop 3319may be configured to provide a main control signal PWM_(DC) forcontrolling the main switching converter 3316 in response the transientcondition.

The auxiliary control loop 3321 includes a feedback and compensationcircuit 3320 and an auxiliary control circuit 3324. The feedback andcompensation circuit 3320 at one end is coupled to the main converterinput capacitor 3317 and the input power source 3310 through theinductor 3315 and at another end is coupled to the auxiliary controlcircuit 3324. The feedback and compensation circuit 3320 includes atransient detection circuit 3322, an error amplifier 3323, and acompensation circuit 3325. The transient detection circuit 3322 includesresistors 3322 a-3322 d. The resistors 3322 a and 3322 b form a firstresistor divider to provide a feedback voltage of the main converterinput capacitor 3317. The resistors 3322 c and 3322 d form a secondresistor divider with the same dividing ratio of the first resistordivider. There is an additional capacitor 3322 e in parallel withresistor 3322 d. The resistor 3322 c, 3322 d and capacitor 3322 e formsa low pass filter so that the voltage on capacitor 3322 e is the lowfrequency average feedback voltage of the main converter input capacitor3317.

The resistors 3322 a at one end is coupled to the main converter inputcapacitor 3317 and input power source 3310 through the inductor 3315 andat another end is coupled to the resistor 3322 b and the invertingterminal of the error amplifier 3323. The resistor 3322 b at one end iscoupled to the resistor 3322 a and the inverting terminal of the erroramplifier 3323 and at another end is coupled to the ground terminal. Theresistor 3322 c at one end is coupled to the main converter inputcapacitor 3317 and the input power source 3310 through the inductor 3315and at another end is coupled to the resistor 3322 d and thenon-inverting terminal of the error amplifier 3323. The resistor 3322 dat one end is coupled to the resistor 3322 c and the non-invertingterminal of the error amplifier 3323 and at another end is coupled tothe ground terminal. The capacitor 3322 e at one end is coupled to thenon-inverting terminal of the error amplifier 3323 and at another end iscoupled to the ground.

The error amplifier 3323 monitors the feedback input voltage of thepower source 3310 with respect to the filtered average feedback inputvoltage of the capacitor 3322 e. When there is a transient conditionsuch as input power source failure, these two voltages are notsubstantially equal to each other and the error amplifier 3323 mayprovide a control signal at its output. The control signal of the erroramplifier 3323 may correspond to the difference between the actual inputvoltage and the desired input voltage.

The compensation circuit 3325 includes capacitors 3325 a and 3325 b anda resistor 3325 c to provide frequency compensation for the feedbackloop. The capacitor 3325 a is connected at one end to an output of theerror amplifier 3323 and at another end to the ground terminal. Theresistor 3325 c is connected at one end to the output of the erroramplifier 3323 and at another end to the capacitor 3325 b. The capacitor3325 b at one end is connected to the resistor 3325 c and at another endto the ground terminal.

The output of the feedback and regulation circuit 3325 is provided tothe auxiliary control circuit 3324. The auxiliary control circuit 3324is configured to generate an auxiliary control signal PWM_(AC) forcontrolling the auxiliary switching converter 3318. The auxiliarycontrol circuit 3324 is similar to the auxiliary control circuit 2924shown in FIG. 29. Therefore, for the sake of brevity of description, itis not described in more details. Based on the auxiliary control signalPWM_(AC), the auxiliary switching converter 3318 sources or sinkscurrent to the main converter input capacitor 3317. For example, whenthere is a temporary failure in the power source 3310, the auxiliarycontrol signal PWM_(AC) may turn ON the first auxiliary switch 3318 a ONand may turn OFF the second auxiliary switch 3318 b. As a result, thepower source 3311 is coupled to the main converter input capacitor 3317through the auxiliary conductor 3318 and high frequency current issupplied to the main converter input capacitor 3317 to maintain theinput voltage V_(IN) _(_) _(DC) at a regulated level. In this manner,the output voltage of the power supply system 3300 may not change inresponse to the temporary failure of the power source 3310. The voltageof the power source 3311 may reduce in response to sourcing additionalcurrent to the main converter input capacitor 3317.

The auxiliary input voltage source control loop 3330 monitors thevoltage of the power source 3311. The auxiliary input voltage sourcecontrol loop 3330 at one end is connected to the power source 3311 andat the other end to the auxiliary control circuit 3324 for driving theauxiliary switching converter 3318. The auxiliary input voltage sourcecontrol loop 3330 is similar to the auxiliary input voltage sourcecontrol loop 2930. Therefore, for the sake of brevity of description, itis not described in more details. In the case of power source 3311 fallsbelow a reference voltage V_(ref), the error amplifier of the controlloop 3330 increases its output voltage, therefore decreases the voltageon the non-inverting terminal of the comparator of the auxiliary controlcircuit 3324 through the second gain buffer. As a result, the auxiliaryinductor 3318 c provides negative current to charge capacitor 3311 fromthe input source 3310 and raises the V_(AC) voltage back to theregulated level. On the other hand, if the V_(AC) voltage on capacitor3311 is higher than the regulated level, the error amplifier the controlloop 3330 decreases its output voltage, therefore increases the voltageon the non-inverting terminal of the comparator of the auxiliary controlcircuit 3324 through the second gain buffer. As a result, the auxiliaryinductor 2918 c provides current from capacitor 3311 to the mainconverter input capacitor 3317 to discharge the V_(AC) voltage back tothe regulated level.

FIG. 34A illustrates simulation waveforms of a conventional supplyhaving a large input voltage ripple during load transient. FIG. 34Billustrates simulation waveform of a power supply system shown in FIG.33, which is configured to reduce the input voltage ripple during loadtransient. Specifically, FIG. 34A-1 illustrates inductor current of theconventional supply system in response to the current load step. FIG.34A-2 illustrates the input voltage ripple of the conventional supplysystem in response to the current load step. FIG. 34A-3 illustrates theoutput voltage rippled in response to the current load step. FIG. 34B-1illustrates the inductor 3316 c current of the main switching converter3316 shown in FIG. 33 in response to the current load step. FIG. 34B-1also illustrates the inductor 3318 c current of the auxiliary switchingconverter 3318 shown in FIG. 33 in response to the current load step.FIG. 34B-2 illustrates the reduced input voltage ripple of the powersource 3310 in response to the current load step. FIG. 34B-3 illustratesthe output voltage ripple of the power supply system 3300 in response tothe current load step.

FIG. 35 illustrates a power supply system 3500 for which current orvoltage transient is predictable by the load device or the applicationsystem. If the load transient is predicable, it is possible to make thefast supply (e.g., auxiliary supply) a controlled AC current source. Ifthe load current step is known ahead of the transient event, the ACcontrol signal is high frequency part of the load step.

The power supply system 3500 includes an input power source 3510, a mainsupply 3514, an auxiliary supply 3516, a load device 3512, and aconverter 3518. The power source 3510 is configured to output a certainstandard voltage. The power source 3510 may be an electrical outlet.Most single phase alternating-current electrical outlets in the worldsupply power at 210-240 V or at 100-120 V. Alternatively, the powersource 3510 may include other types of power sources such as, forexample, a battery, a solar photovoltaic, an AC generator, or a DCoutput voltage of a front-end power supply. Regardless of the type,usually the power source 3510 provides a voltage different than therequired voltage for the load device 3512. The provided voltage may behigher or lower than the required voltage for the load device 3512. Tomatch the source voltage to the load voltage, the power supply system3500 includes the main supply 3514 and an auxiliary supply 3516.

The main supply 3514 and the auxiliary supply 3516 are configured tochange their respective input voltages to an appropriate voltage for theload device 3512. The appropriate voltage for the load device 3512 maybe higher or lower than the input voltages of the main supply 3514 andthe auxiliary supply 3516. In one implementation, the appropriatevoltage for the load device 3512 is lower than the voltage of theelectrical power sources for the main supply 3514 and the auxiliarysupply 3516. The load device 3512 may include a resistive load, amagnetic load, a capacitive load, a heater, or modern electronicdevices.

Although not shown, the main supply 3514 includes a main switchingconverter and a main supply feedback control loop. The main switchingconverter of the main supply 3514 is similar to the main switchingconverter 2916 described with respect to FIG. 29. The main supplyfeedback control loop of the main supply 3514 is similar to the mainsupply feedback control loop 2919 described with respect to FIG. 29.

The auxiliary supply 3516 at one end is coupled to the load device 3512and at another end is coupled to a power source 3511. The power source3511 includes a capacitive power source. The power source 3511 maysupply power at a lower voltage than the power source 3510. The powersource 3511 may only supply high frequency transient current. The powersource 3511 is coupled to the power source 3510 through a converter3513. The converter 3513 may be a DC-DC converter and configured toreduce the input voltage of the power source 3510 for the auxiliarysupply 3516. This is done to reduce the power loss associated with theauxiliary supply 3516 due to its higher switching frequency. Althoughnot shown, the auxiliary supply 3516 includes an auxiliary switchingconverter, an auxiliary supply feedback control loop, and an auxiliaryinput voltage source control loop. The auxiliary switching converter,the auxiliary supply feedback control loop, and the auxiliary inputvoltage source control loop respectively are the same as auxiliaryswitching converter 2918, the auxiliary control loop 2921, and theauxiliary input voltage source 2930 shown and described with respect toFIG. 29 except an additional current control signal from the load deviceor the application system is injected to the auxiliary supply to changeits AC output current quickly to meet the coming load transientrequirement. Therefore, for the sake of brevity, they are not describedfurther.

While the foregoing has described what are considered to be the bestmode and/or other examples, it is understood that various modificationsmay be made therein and that the subject matter disclosed herein may beimplemented in various forms and examples, and that the teachings may beapplied in numerous applications, only some of which have been describedherein. It is intended by the following claims to claim any and allapplications, modifications and variations that fall within the truescope of the present teachings.

Unless otherwise stated, all measurements, values, ratings, positions,magnitudes, sizes, and other specifications that are set forth in thisspecification, including in the claims that follow, are approximate, notexact. They are intended to have a reasonable range that is consistentwith the functions to which they relate and with what is customary inthe art to which they pertain.

The scope of protection is limited solely by the claims that now follow.That scope is intended and should be interpreted to be as broad as isconsistent with the ordinary meaning of the language that is used in theclaims when interpreted in light of this specification and theprosecution history that follows and to encompass all structural andfunctional equivalents. Notwithstanding, none of the claims are intendedto embrace subject matter that fails to satisfy the requirement ofSections 101, 102, or 103 of the patent Act, nor should they beinterpreted in such a way. Any unintended embracement of such subjectmatter is hereby disclaimed.

Except as stated immediately above, nothing that has been stated orillustrated is intended or should be interpreted to cause a dedicationof any component, step, feature, object, benefit, advantage, orequivalent to the public, regardless of whether it is or is not recitedin the claims.

It will be understood that the terms and expressions used herein havethe ordinary meaning as is accorded to such terms and expressions withrespect to their corresponding respective areas of inquiry and studyexcept where specific meanings have otherwise been set forth herein.Relational terms such as first and second and the like may be usedsolely to distinguish one entity or action from another withoutnecessarily requiring or implying any actual such relationship or orderbetween such entities or actions. The terms “comprises,” “comprising,”or any other variation thereof, are intended to cover a non-exclusiveinclusion, such that a process, method, article, or apparatus thatcomprises a list of elements does not include only those elements butmay include other elements not expressly listed or inherent to suchprocess, method, article, or apparatus. An element proceeded by “a” or“an” does not, without further constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises the element.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various examples for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claims require more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed example. Thus the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separately claimed subject matter.

What is claimed is:
 1. A power interface device coupled to a powersource for adjusting a voltage of the power source to correspond to avoltage associated with a load device, the power interface devicecomprising: a main control circuit including a low pass filterconfigured to receive a transient signal, the main control circuit beingconfigured to generate, based on a lower frequency component of thetransient signal received at an output terminal, a main control signalfor controlling a main switching converter coupled to the outputterminal; an auxiliary control circuit including a high pass filterconfigured to receive the transient signal, the auxiliary controlcircuit configured to generate, based on a higher frequency component ofthe transient signal, an auxiliary control signal for controlling anauxiliary switching converter coupled to the output terminal, whereinthe auxiliary switching converter operates at a higher switchingfrequency than the main switching converter; and a common buffercommonly shared by the main control circuit and the auxiliary controlcircuit.
 2. The power interface device of claim 1, further comprising: afeedback sense circuit configured to sense an output voltage at theoutput terminal; an error amplifier configured to output the transientsignal based on the sensed output voltage and a reference voltage; and acompensation circuit configured to receive the transient signal and tooutput a frequency compensated transient signal to the common buffer. 3.The power interface device of claim 2, wherein: the feedback sensecircuit comprises one or more resistors and one or more capacitorsconfigured to sense the output voltage and generate a feedback voltage,and the error amplifier is configured to receive the feedback voltageand the reference voltage, and generate the transient signal when thefeedback voltage and the reference voltage are not substantially equalto each other.
 4. The power interface device of claim 2, wherein: thecompensation circuit includes a capacitor-resistor network comprising afirst capacitor, a second capacitor, and a resistor, the first capacitorbeing connected at one end to an output terminal of the error amplifierand at another end being connected to a ground terminal, the secondcapacitor being connected in series with the resistor forming a seriescapacitor-resistor network, wherein the series capacitor-resistornetwork is connected to the ground terminal at one end, and to theoutput terminal of the error amplifier at another end.
 5. The powerinterface device of claim 1, wherein: the main control circuit comprisesa main comparator configured to compare the lower frequency component ofthe transient signal with a sensed low frequency inductor signal sourcedby the main switching converter, the main control signal being generatedbased on comparing the lower frequency component and the sensed lowfrequency inductor signal, and the main control signal enables the mainswitching converter to source to the output terminal a low frequencycurrent tracking the lower frequency component of the transient signal.6. The power interface device of claim 5, wherein: the auxiliary controlcircuit comprises an auxiliary comparator configured to compare thehigher frequency component of the transient signal with a sensed highfrequency inductor signal sourced by the auxiliary switching converter,the auxiliary control signal being generated based on comparing the highfrequency component and the sensed high frequency inductor signal, theauxiliary control signal enables the auxiliary switching converter tosource to the output terminal a high frequency current tracking thehigher frequency component of the transient signal.
 7. The powerinterface device of claim 6, wherein a resistor of the low pass filteris connected at one end to the common buffer and at another end to acapacitor of the low pass filter and a non-inverting terminal of themain comparator, and the capacitor of the low pass filter is connectedat one end to the resistor of the low pass filter and the non-invertingterminal of the main comparator and at another end is connected to theground terminal, and wherein a capacitor of the high pass filter isconnected at one end to the common buffer and at another end to aresistor of the high pass filter and a non-inverting terminal of theauxiliary comparator, and the resistor of the high pass filter isconnected at one end to a capacitor of the high pass filter and thenon-inverting terminal of the auxiliary comparator and at another end isconnected to the ground terminal.
 8. The power interface device of claim1, further comprising: a feedback and compensation circuit configured todetect a transient condition at the output terminal and generate thetransient signal based on the detected transient condition, wherein thecommon buffer comprises an input terminal and an output terminal, theinput terminal being connected to the feedback and compensation circuit,and the output terminal being connected to the high pass filter and thelow pass filter.
 9. The power interface device of claim 1, furthercomprising: a feedback and compensation circuit configured to detect atransient condition at the output terminal and generate the transientsignal based on the detected transient condition, wherein the commonbuffer is configured to isolate the main control circuit and theauxiliary control circuit from an impedance of the feedback andcompensation circuit.
 10. The power interface device of claim 9,wherein: the main switching converter is configured to source, to theoutput terminal, low frequency current during the transient conditionand outside the transient condition, the auxiliary switching converteris configured to source, to the output terminal, high frequency currentduring the transient condition and substantially zero average currentoutside the transient condition, and the transient condition includes asudden increase or decrease in load current, or a sudden increase ordecrease of an output voltage.
 11. A power interface device comprising:a feedback and compensation circuit configured to output a transientsignal based on a transient condition detected at an output terminal; ahigh pass filter configured to output a higher frequency component ofthe transient signal; an adder circuit configured to receive the higherfrequency component of the transient signal from the high pass filterand the transient signal from the feedback and compensation circuit andto output a lower frequency component of the transient signal;configured to generate, based on the lower frequency component of thetransient signal, a main control signal for controlling a main switchingconverter coupled to the output terminal; and an auxiliary controlcircuit configured to generate, based on the higher frequency componentof the transient signal, an auxiliary control signal for controlling anauxiliary switching converter coupled to the output terminal, whereinthe auxiliary switching converter operates at a higher switchingfrequency than the main switching converter.
 12. A power interfacedevice comprising: a feedback and compensation circuit configured todetect a transient condition at an output terminal and to output atransient signal based on the detected transient condition; a maincontrol circuit configured to receive the transient signal from thefeedback and compensation circuit and to generate, based on thetransient signal, a main control signal for controlling a main switchingconverter coupled to the output terminal; a low pass filter configuredto receive the transient signal from the feedback and compensationcircuit and to output a lower frequency component of the transientsignal; an adder circuit configured to receive the lower frequencycomponent of the transient signal from the low pass filter and thetransient signal from the feedback and compensation circuit and tooutput a higher frequency component of the transient signal; and anauxiliary control circuit configured to receive the higher frequencycomponent of the transient signal from the adder circuit and togenerate, based on the higher frequency component of the transientsignal, an auxiliary control signal for controlling an auxiliaryswitching converter coupled to the output terminal, wherein theauxiliary switching converter operates at a higher switching frequencythan the main switching converter.
 13. The power interface device ofclaim 12, wherein the adder circuit is configured to receive the lowerfrequency component of the transient signal from the low pass filter andthe transient signal from the feedback and compensation circuit,determine a difference between the lower frequency component of thetransient signal and the transient signal, and output the higherfrequency component of the transient signal to the auxiliary controlcircuit based on the determined difference.
 14. The power interfacedevice of claim 13, further comprising a buffer between the feedback andcompensation circuit and the auxiliary control circuit and configured tothe auxiliary control circuit from an impedance of the feedback andcompensation circuit.
 15. The power interface device of claim 14,wherein: the low pass filter includes a resistor and a capacitor, theresistor is coupled to an output terminal of the buffer at one end andto a first node at a second end, the capacitor is connected to the firstnode at one end and to a ground terminal at another end, and the addercircuit is coupled to the first node and to the output terminal of thefeedback and compensation circuit, and is configured to receive thelower frequency component of the transient signal from the low passfilter and the transient signal from the feedback and compensationcircuit, and output the higher frequency component of the transientsignal to the auxiliary control circuit based on the received lowerfrequency component and the received transient signal.
 16. The powerinterface device of claim 15, further comprising: an offset voltagesource configured to offset high frequency current sourced by theauxiliary switching converter outside the transient condition during asteady state to enable sourcing substantially zero average current fromthe auxiliary switching converter, wherein the offset voltage source iscoupled to the adder circuit via a first resistor.
 17. A power interfacedevice comprising: a feedback and compensation circuit configured todetect a transient condition of a main switching converter and to outputa transient signal based on a detected transient condition; configuredto receive the transient signal from the feedback and compensationcircuit and to control the main switching converter based on thetransient signal; and an auxiliary control circuit including: a firstgain buffer configured to amplify the transient signal, a high passfilter configured to output a higher frequency component of theamplified transient signal, and an auxiliary comparator configured toreceive at a first terminal the higher frequency component of thetransient signal and a sensed high frequency inductor signal at a secondterminal from an auxiliary switching converter, and configured tocontrol the auxiliary switching converter based on a comparison of thehigher frequency component and the sensed high frequency inductorsignal, wherein the auxiliary switching converter operates at a higherswitching frequency than the main switching converter.
 18. The powerinterface device of claim 17, wherein the power interface device furtherincludes an offset voltage source coupled to the high pass filter andconfigured to offset high frequency current sourced by the auxiliaryswitching converter to enable sourcing substantially zero averagecurrent from the auxiliary switching converter outside of the transientcondition.
 19. A power supply system comprising: the power interfacedevice of claim 17 coupled to a first power source and a second powersource and load device, and configured to adjust a voltage of the firstpower source to correspond to a voltage of the load device, wherein: thefirst power source is coupled to the main switching converter, and thesecond power source is coupled to the auxiliary switching converter andis independent from the first power source.
 20. The power supply systemof claim 19, wherein the second power source is a capacitor.
 21. Thepower supply system of claim 20, further comprising: an input sourcefeedback and regulation circuit connected at one end to the second powersource and at another end to the auxiliary control circuit wherein theinput source feedback and regulation circuit includes a feedback voltagesense circuit, an error amplifier, and a compensation circuit, andwherein: the feedback voltage sense circuit is configured to sense thevoltage of the second power source and output a feedback voltage to afirst terminal of the error amplifier, and the error amplifier isconfigured to monitor the feedback voltage received at the firstterminal of the error amplifier and a reference voltage received at asecond terminal of the error amplifier, and output a control signal whenthe feedback voltage is not substantially equal to the referencevoltage.
 22. The power supply system of claim 21, wherein: the auxiliarycontrol circuit further includes a second gain buffer connected to anoutput terminal of the error amplifier which regulates a voltage of thesecond power source, an the output terminal of the second gain bufferbeing connected to the high pass filter, and when the voltage of thesecond power source falls below the reference voltage, the erroramplifier increases the control signal, thereby decreasing signal on thefirst terminal of the auxiliary comparator through the second gainbuffer which in turn results in current flowing from the output terminalthrough the auxiliary switching converter to the second power source tocharge the second power source.
 23. A power interface device comprising:a compensation circuit configured to detect a transient condition at anoutput terminal and to output a transient signal based on the detectedtransient condition; a first buffer coupled to the compensation circuit;low pass filter including a resistor and a capacitor, wherein theresistor is coupled to and between the first buffer and the capacitor,and the capacitor is coupled to a ground terminal; a main controlcircuit including a main comparator configured to receive a lowerfrequency component of the transient signal from the low pass filter anda sensed inductor current signal of a main switching converterconfigured to source current from an input terminal to the outputterminal, and to control the main switching converter based on the lowerfrequency component of the transient signal; and an auxiliary controlcircuit including a gain buffer and an auxiliary comparator, wherein:the gain buffer includes a first terminal coupled to an output of thefirst buffer and a second terminal coupled to the capacitor andconfigured to provide a higher frequency component of the transientsignal to the auxiliary comparator, the auxiliary comparator isconfigured to compare the higher frequency component of the transientsignal and a sensed high frequency inductor current provided by anauxiliary switching converter coupled to the output terminal, and tocontrol the auxiliary switching converter based on comparing the higherfrequency component and the sensed high frequency inductor current,wherein the auxiliary switching converter operates at a higher switchingfrequency than the main switching converter.
 24. The power interfacedevice of claim 23, wherein: during a load step up transient condition,the auxiliary comparator generates a high auxiliary control signal forsourcing high frequency current from the input terminal to the outputterminal to improve transient response and reduce output voltage rippledue to the transient condition and the main comparator circuit generatesa high main control signal for sourcing low frequency current from theinput terminal to the output terminal, the high frequency current tracksthe higher frequency component of the transient signal, and the lowfrequency current tracks the lower frequency component of the transientsignal.
 25. The power interface device of claim 23, wherein: during aload step up transient condition, the auxiliary comparator generates ahigh auxiliary control signal for sourcing high frequency current fromthe input terminal to the output terminal to improve transient responseand reduce output voltage ripple due to the transient condition and themain comparator circuit generates a high main control signal forsourcing low frequency current from the input terminal to the outputterminal, the high frequency current tracks the higher frequencycomponent of the transient signal, and the low frequency current tracksthe lower frequency component of the transient signal.
 26. A powerinterface device comprising: a feedback and compensation circuitconfigured to detect a transient condition at an output terminal and tooutput a transient signal based on a detected transient condition; amain control circuit configured to receive the transient signal from thefeedback and compensation circuit and to control a main switchingconverter configured to operate at a first frequency to source currentfrom an input terminal to an output terminal based on the transientsignal; an auxiliary control circuit configured to receive a higherfrequency component of the transient signal from the feedback-andcompensation circuit and to control an auxiliary switching converterconfigured to operate at a second frequency to source current from theinput terminal to the output terminal based on the higher frequencycomponent of the transient signal, wherein the auxiliary switchingconverter operates at a higher switching frequency than the mainswitching converter, and wherein: the feedback and compensation circuitincludes: a feedback sense circuit configured to sense an output voltageof the main switching converter and to generate a feedback voltage, andan error amplifier configured to receive the feedback voltage and areference voltage and output the transient signal based on a sensedoutput voltage and the reference voltage.
 27. The power interface deviceof claim 26, wherein the feedback and compensation circuit furtherincludes a compensation circuit, and wherein the auxiliary controlcircuit includes an auxiliary comparator configured to receive a higherfrequency component of the transient signal and sensed high frequencyinductor current from the auxiliary switching converter, and to generatean auxiliary control signal to control the auxiliary switchingconverter.
 28. The power interface device of claim 27, wherein: during aload step up transient condition, the auxiliary comparator generates ahigh auxiliary control signal for sourcing high frequency current fromthe input terminal to the output terminal to improve transient responseand reduce output voltage ripple due to the transient condition and themain control circuit generates a high main control signal for sourcinglow frequency current from the input terminal to the output terminal,the high frequency current tracks a higher frequency component of thetransient signal, and the low frequency current tracks a lower frequencycomponent of the transient signal.
 29. The power interface device ofclaim 27, wherein: during a load step up transient condition, theauxiliary comparator generates a high auxiliary control signal forsourcing high frequency current from the input terminal to the outputterminal to improve transient response and reduce output voltage rippledue to the transient condition and the main control circuit generates ahigh main control signal for sourcing low frequency current from theinput terminal to the output terminal, the high frequency current tracksa higher frequency component of the transient signal, and the lowfrequency current tracks a lower frequency component of the transientsignal.
 30. A power interface device comprising: a feedback andcompensation circuit and configured to detect a transient condition atan output terminal and to output a transient signal based on a detectedtransient condition; a main control circuit configured to generate,based on the transient signal, a main control signal for controllingmain switching converter configured to source current from an inputterminal to the output terminal; a resistor-capacitor (“RC”) and addernetwork coupled to the feedback and compensation circuit and configuredto receive the transient signal from the feedback and compensationcircuit and output a higher frequency component of the transient signal;and an auxiliary control circuit coupled to the RC and adder network andan auxiliary switching converter configured to source current from theinput terminal to the output terminal, the auxiliary control circuitconfigured to receive the higher frequency component of the transientsignal and to generate, based on the higher frequency component of thetransient signal, an auxiliary control signal for controlling anauxiliary switching converter coupled to the output terminal, whereinthe auxiliary switching converter operates at a higher switchingfrequency than the main switching converter.
 31. The power interfacedevice of claim 30, wherein: the RC and adder network includes a highpass filter and an adder circuit, the high pass filter is coupled to thefeedback and compensation circuit and configured to receive thetransient signal from the feedback and compensation circuit and outputthe higher frequency component of the transient signal to the auxiliarycontrol circuit, the adder circuit is coupled to the high pass filterand the feedback and compensation circuit and configured to receive thehigher frequency component of the transient signal from the high passfilter and the transient signal from the feedback and compensationcircuit and output a lower frequency component of the transient signalto the main control circuit, and the main control circuit is configuredto generate the main control signal based on the lower frequencycomponent of the transient signal.
 32. The power interface device ofclaim 30, wherein: the RC and adder network includes a low pass filterand an adder circuit, the low pass filter is coupled to the feedback andcompensation circuit and configured to receive the transient signal fromthe feedback and compensation circuit and output a lower frequencycomponent of the transient signal, the adder circuit is coupled to thelow pass filter and the feedback and compensation circuit and configuredto receive the lower frequency component of the transient signal fromthe low pass filter and the transient signal from the feedback andcompensation circuit and output the higher frequency component of thetransient signal to the auxiliary control circuit.
 33. A power supplysystem comprising: a main control loop coupled to a main switchingconverter, and configured to detect a transient condition at an outputterminal and to generate, based on a detected transient condition, amain control signal for controlling a main switching converter coupledto the output terminal and configured to source current from a firstinput terminal; and an auxiliary control loop configured to detect thetransient condition and to generate, based on the detected transientcondition, an auxiliary control signal or controlling an auxiliaryswitching converter coupled to the output terminal and configured tosource current from a second input terminal, wherein the auxiliaryswitching converter operates at a higher switching frequency than themain switching converter, and wherein: the auxiliary control loopincludes an auxiliary feedback and compensation circuit, a first gainbuffer, and a high pass filter, the auxiliary feedback and compensationcircuit is configured to detect the transient condition and output anauxiliary transient signal based on the detected transient condition,the first gain buffer is coupled to the auxiliary feedback andcompensation circuit and configured to amplify the auxiliary transientsignal received from the auxiliary feedback and compensation circuit,and the high pass filter is coupled to the first gain buffer andconfigured to receive the amplified auxiliary transient signal from thefirst gain buffer and output a higher frequency component of theamplified auxiliary transient signal.
 34. The power supply system ofclaim 33, wherein the main control loop includes: a main feedback andcompensation circuit coupled to the output terminal and configured todetect the transient condition at the output terminal and output a maintransient signal based on the detected transient condition, and a maincomparator coupled to the main feedback and compensation circuit and themain switching converter and configured to receive the main transientsignal from the main feedback and compensation circuit and generate themain control signal based on the main transient signal for controllingthe main switching converter.
 35. The power supply system of claim 33,wherein: the auxiliary feedback and compensation circuit is coupled tothe output terminal and configured to detect the transient condition atthe output terminal and output the auxiliary transient signal based onthe detected transient condition, wherein the auxiliary control signalis generated based on a comparison result of the higher frequencycomponent of the amplified auxiliary transient signal and a sensed highfrequency inductor signal sourced by the auxiliary switching converter.36. The power supply system of claim 33, wherein the auxiliary controlloop further includes a second gain buffer, the power supply systemfurther comprising: an input source feedback and regulation circuitconnected at one end to the second input terminal and at another end toan input terminal of second gain buffer for controlling the auxiliaryswitching converter, wherein the input source feedback and regulationcircuit includes a feedback voltage sense circuit, and an erroramplifier, wherein: the feedback voltage sense circuit is configured tosense a voltage at the second input terminal and output a feedbackvoltage to a first input terminal of the error amplifier, the erroramplifier being configured to monitor the feedback voltage received atthe a first input terminal of the error amplifier and a referencevoltage received at a second terminal of the error amplifier, and tooutput a control signal when the feedback voltage is not substantiallyequal to the reference voltage.
 37. The power supply system of claim 36,wherein the auxiliary control loop includes an auxiliary comparatorconnected to the high pass filter and configured to receive the higherfrequency component of the auxiliary transient signal at a firstterminal and a sensed high frequency inductor signal sourced by theauxiliary switching converter at a second terminal, and to generate theauxiliary control signal based on comparison result of the higherfrequency component and the sensed high frequency inductor signal forcontrolling the auxiliary switching converter.
 38. The power supplysystem of claim 37, wherein: when a voltage at the second input terminalfalls below a reference voltage, the error amplifier increases thecontrol signal, thereby decreasing signal on the first terminal of theauxiliary comparator through the second gain buffer which in turnresults in current flowing from the output terminal through theauxiliary switching converter to an auxiliary power source connected tothe second input terminal to charge the auxiliary power source, and theauxiliary power source includes a capacitor.
 39. The power supply systemof claim 36, wherein the input source feedback and regulation circuitincludes a compensation circuit, wherein the compensation circuitincludes a first and second capacitors and a resistor, the firstcapacitor being connected at one end to an output of the error amplifierand at another end to the ground terminal, the resistor of thecompensation circuit being connected at one end to the output of theerror amplifier and at another end to the second capacitor, the secondcapacitor at one end being connected to the resistor of the compensationcircuit and at another end to the ground terminal, and the inputterminal of the second gain buffer being connected to the output of theerror amplifier which regulates a voltage at the second input terminal.40. The power supply system of claim 33, further comprising: a mainpower source coupled to the first input terminal; an auxiliary powersource coupled to the second input terminal; and a load device coupledto the output terminal, wherein the main power source is coupled to themain switching converter, the auxiliary power source is coupled to theauxiliary switching converter and is independent from the main powersource, the main switching converter is configured to change a voltageof the main power source to correspond to a voltage of the load device.41. The power supply system of claim 40, wherein: the auxiliary feedbackand compensation circuit is coupled to the first input terminal andconfigured to detect the transient condition at the first input terminaland output the auxiliary transient signal based on the detectedtransient condition at the first input terminal, and the transientcondition at the first input terminal includes temporary loss of voltageat the first input terminal.